The disorder suffered by the protagonist, dissociative identity disorder is an actual mental health problem. When the symptoms of the illness are explained, its most famous case is shown, that of an American woman named Shirley Ardell Mason.
Badri (Manoj Joshi) heads a Brahmin family whose ancestral palace is believed to be haunted by the ghost of Manjulika, a Bengali classical dancer. Siddharth (Shiney Ahuja) and Avni (Vidya Balan), the son and daughter-in-law of Badri's elder brother, return to their native village from United States and decide to stay in their ancestral palace. This leads to Siddharth's childhood love interest Radha (Ameesha Patel), who is Badri's Daughter, becoming jealous but she immediately recovers. Siddharth is crowned as the king, his right to the throne.
The palace where Siddharth and Avni were staying was once occupied by Raja Vibhuti Narayan, who was Siddharth's ancestor. He had fallen in love with Manjulika, a dancer hailing from Bengal. But Manjulika was in love with Shashidhar, another dancer, who resided in a house just behind the palace and often met her secretly. On the night of Durgashtami, when the king gets to know of the affair and their plan to elope, he calls them to perform a dance one last time in the court. In the end, the king beheads Shashidhar and imprisons Manjulika in her room. Then on the day of the king's marriage, Manjulika hangs herself and swore that her spirit would not leave any king who lived in that very palace. Various omens started taking place after that, presuming that the "evil eye" may have befallen on the king. The king too dies under unknown circumstances. Soon, with the aid of powerful sorcerers, both Vibhuti's and Manjulika's spirits were locked up in a room in the third floor of the palace using a sacred talisman.
Events take a twist when Avni obtains a copy of the third floor room key and opens the forbidden locked room that contains the ghost of Manjulika. Unnatural events start taking place inside the palace. Avni falls in love with the place and learns about Manjulika and her tragic story. She becomes enamored with Manjulika. Badri and Batuk Shankar (Paresh Rawal) try to ward off the evil eye with the help of a priest, Shri Yagyaprakashji Bharti (Vikram Gokhale), but unfortunately the priest has gone to London and is unsure when he might return.
Siddharth starts suspecting Radha for all the strange occurrences. He thinks she has gone crazy since he was supposed to marry her, but married Avni instead. He calls his friend, psychiatrist Dr. Aditya Shrivastav (Akshay Kumar) from New York, to try to figure out what the problem is with Radha. Once Aditya reaches the palace, things become comical, as everyone thinks he is a fool, though he is very intelligent. Aditya eventually realizes that Radha is not at fault, and that someone else behind it all, and falls in love with her. One night, he encounters Manjulika and dares her to strike. The ghost angrily vows to take her revenge on the auspicious day of Durgashtami.
During the engagement of Siddharth's cousin Nandini, and Sharad Pradhan (Vineeth), Avni spills food on Sharad and takes him away to get him cleaned. When Aditya and Siddharth search for her, they see that there is a struggle between Avni and Sharad, and quickly intervene. Siddharth thinks that Sharad was violating Avni, but Aditya tells him that Avni is the real culprit, not Radha as previously suspected. It is revealed that Avni has dissociative identity disorder, a disease that affects the person's identity, making them think they're someone else. Aditya explains that Avni is the one making all the strange things happen around the palace. He reveals that he visited Avni's hometown to gather information about her childhood and has factual evidence. He then tells the half-convinced Siddtharth to provoke Avni in order to make him realize that something is wrong. When Siddharth provokes her, Avni shows the dark personality of Manjulika before returning to her usual self, much to the horror and concern of Siddharth, who asks Aditya to save Avni.
During Durgashtami, Aditya and Siddharth see Avni consumed in Manjulika's identity, dressed as her and dancing to the tunes Manjulika had been dancing to with her love, Shashidhar, before the king murdered him. The tragic love story of the old king Vibhuti Narayan, who loved Manjulika, who in turn loved Shashidhar, is revealed. Avni imagines herself as Manjulika and Sharad as Shashidhar, dancing in the court of the king. Avni completely assumes the identity of Manjulika and tries to kill her own husband Siddharth; she sees him as the king who had killed Manjulika's lover.
To cure Avni, Aditya triggers Manjulika's personality and makes her promise to leave Avni if she gets the opportunity to kill the king and take her revenge. The priest Shri Yagyaprakashji Bharti arrives and with his help, during the ritual of Durgashtami, Aditya lays out an intricate plan to trick Manjulika into thinking she is killing the king when she is actually slaying a dummy. After the "murder", Manjulika, now content, leaves Avni forever. Avni is healed and everything ends well. Aditya tells Radha, whom he has taken a liking to, that he will send his parents over if she is interested in marrying him, to which a happy Radha gives her silent consent.Akshay Kumar as Dr. Aditya Shrivastav, Siddharth's friend and a psychiatrist whom Siddharth calls upon to check the happenings in the haveli
Vidya Balan as Avni Chaturvedi/Manjulika, A young woman who marries Siddharth. After she opens the locked room where the family believes Manjulika's spirit has been trapped, mysterious and supernatural happenings begin in the house
Shiney Ahuja as Siddharth Chaturvedi, Avni's loving husband who is educated in the United States. Unlike his family, he doesn't believe in the supernatural, and thus calls his friend and psychiatrist Aditya to investigate the matter
Ameesha Patel as Radha, Siddharth's childhood friend and Aditya's love interest. She is suspected by Siddharth as being behind the supernatural happenings, and is used by Aditya to manipulate Manjulika
Paresh Rawal as Batukshankar Upadhyay
Rajpal Yadav as Chhote Pandit / Lal Hanuman
Asrani as Murari
Vikram Gokhale as Acharya Yagyaprakash Bharti
Manoj Joshi as Badrinarayan 'Badri' Chaturvedi
Rasika Joshi as Janki Upadhyay
Tarina Patel as Nandini Upadhyay
Vineeth as Professor Sharad Prahlad / Shashidhar
Kaveri Jha as Girja Upadhyay
Navika Kotia as child Avni
Jimit Trivedi as Goti
Originally Aishwarya Rai and Katrina Kaif were the first female choices for Bhool Bhulaiyaa. They turned down the offer and were replaced by Vidya Balan and Ameesha Patel. Vidya Balan had to take Kathak lessons for this film. Incidentally, Vineeth played the same role in the Rajinikanth-starrer Chandramukhi (2005), which was the Tamil remake of Manichithrathazhu. The dance consisted mainly of a fusion of kathak, odissi and bharatanatyam.
The film score was composed and produced by Ranjit Barot.
The soundtrack, composed by Pritam, was released in September 2007. According to the Indian trade website Box Office India, with around 12,00,000 units sold, this film's soundtrack album was the year's eighth highest-selling.
All lyrics written by Sameer and Sayeed Quadri.
Bhool Bhulaiyaa was a commercial success, netting ₹497 million (US$7.7 million) in India. It was the 6th highest domestic grosser of 2007.
The total overseas gross was $3,910,000. The lifetime overseas breakup was $1,380,000 in UK, $1,130,000 in North America, $820,000 in UAE, $151,000 in Australia and $429,000 in other markets.
The film collected ₹840 million (US$13 million) worldwide.