Introduction and objectives: The use of substances, drugs and methods to improve work or sports performance has been well known for centuries. However, the International Olympic Committee only carried out the first anti-doping tests in the Mexico Olympic Games (1968). The main objective of this study is to analyse the evolution of the anti-doping tests results since 1968 until the present.Methods: We have reviewed the development of the positive cases at the Summer Olympic Games by the International Olympic Committee and World Anti-Doping Agency Official Web Sites, which have been compared with documents from the specialised press.Results: The total number of anti-doping tests was 21,849, with 94 being penalised. The highest number of positives (26) took place in Athens 2004. By contrast, no positives were found in Moscow 1980. The highest percentage of positive cases per anti-doping tests was found in Montreal 1976 (1.40%). The most sanctioned continent was Europe (62.67% of total cases) and anabolic agents were the most used substances (46 positives). The percentage of athletes tested has risen steeply over the last years (1996: 18.64%; 2008: 42.86%).Conclusions: The number of anti-doping tests has increased since 1980. The creation of the World Anti-Doping Agency and its anti-doping policy could explain the decrease in the positive cases at the Beijing Olympic Games in 2008.