Alla Ivanovna Sizova was born in Moscow on 22 September 1939. Her parents were Ivan and Ekaterina Sizov. The family moved to Leningrad shortly after her birth. During the Second World War, she was evacuated to the Urals with her mother and sister, while her father remained in Leningrad.
After the war, Sizova studied at the Vaganova Academy of Russian Ballet, where she was taught by Natalia Kamkova. Among her classmates was Rudolph Nureyev, with whom she performed the Le Corsaire duet in a school graduation film, which attracted the attention of the Kirov Ballet. The two were recruited by the Kirov directly as soloists.
Despite the immense chemistry on-stage between Sizova and Nureyev which manifested itself in their very successful partnership for the Kirov Ballet, temperamentally they were ill-suited to each other. They were forced to share an apartment but brought in their families to live with them and act as a buffer.
Following Nureyev's defection in 1961 during a tour in London, Sizova's family was closely questioned by the KGB, resulting in her mother's mental breakdown. Upon her return to the USSR, Sizova refused to condemn his actions, although she questioned why he would leave to perform in foreign ballets she considered inferior.
In the early 1970s, Sizova married Mikhail Serebrennikov, a television producer. They had a son, Ilya, born 1974.
Following her husband's death in 1980, Sizova moved to the United States. Sizova's son died in 2004, whereupon she returned to Russia where she led a reclusive life. In the late 2000s, she developed Alzheimer's disease. She died of cancer in St. Petersburg on 23 November 2014.
Sizova joined the Kirov Ballet as soloist in 1958 and became principal shortly after. Her first full part at the Kirov was as Masha in The Nutcracker. Between 1958 and 1961, she performed fourteen major roles. She starred in The Sleeping Beauty and Giselle. The Kirov recognised her talent of musicality and vulnerability, and gave her the leading part in Igor Belsky's balletic setting of Shostakovich's Leningrad Symphony.
Sizova's extraordinary high jumps and technical skills led Leningrad critics to call her Flying Sizova.
After Nureyev's departure, Sizova continued her career with a new partner, Yuri Soloviev, with whom she performed roles of great sensitivity and demonstrated the highest achievement of the Kirov's training.
Between 1964 and 1966, Sizova required extensive treatment for spinal injuries caused by the landings from her high jumps. In the 1970s, her tours with the Kirov in London were widely anticipated and acclaimed.
Sizova's final appearance on-stage was in 1988 in Chopiniana. She then taught for three years at the Vaganov school.
From 1991, Sizova taught at the Kirov Academy of Ballet in Washington, with her ex-Kirov colleague Oleg Vinogradov.
Amongst other roles, Sizova received great acclaim as Princess Aurora in the 1964 Kirov production Tchaikovsky's The Sleeping Beauty opposite Yuri Soloviev.
Nureyev is rumoured to have said in his later years that Sizova was the only thing that could conceivably entice him back to the Soviet Union.
Sizova was awarded the Soviet Union's highest artistic honour, the People's Artist of the USSR in 1983.