Opatija Circuit was a motorsport street circuit located in Opatija, Croatia. The circuit used the city streets of the seaside resort of Opatija between 1939 and 1977. It was known as the "Monaco" of the Grand Prix motorcycle racing circuit because of its spectacular views of the Adriatic Sea.
The Opatija Circuit hosted sportscar races between 1950 and 1959, Formula Junior races in 1960, 1961 and 1963, and Formula 3 races between 1964 and 1968. From 1969 to 1977, it hosted the Yugoslavian Grand Prix as part of the Grand Prix motorcycle racing world championship. When Godfrey Nash rode a Norton Manx to victory at the 1969 Yugoslavian Grand Prix at Opatija, it marked the last victory for a single-cylinder machine in a 500cc Grand Prix.
Despite the circuit's scenic setting, it was an unsafe race track due to high speeds on narrow roads coupled with numerous unmovable roadside obstacles, such as trees, stone walls, lampposts, electric poles, embankments, houses, and the Adriatic Sea. During the 1973 season, several racing teams including Yamaha, Harley Davidson and MV Agusta, boycotted the event due to unsafe track conditions. Other riders chose to compete, but with less than their full efforts. In 1974, British rider Billie Nelson was killed at the event.
The Yugoslavian Grand Prix promoters had received an ultimatum from the FIM before the 1977 Yugoslavian Grand Prix race that, if they did not improve the safety of the circuit, the event would be canceled. The event was a disaster with Italian rider, Giovanni Ziggiotto, crashing during practice for the 250cc race when his motorcycle's engine seized. He was hit by another rider and died four days later in a hospital. During the 50 cc race, Ulrich Graf crashed when his bike developed a rear tire puncture. He suffered serious head injuries and died later in a hospital. The tragedy forced the venue off the Grand Prix schedule and the Yugoslavian Grand Prix was moved to the Rijeka Circuit for the 1978 season.