OBJECTIVE: To examine the relation between frequency of orgasm and mortality. STUDY DESIGN: Cohort study with a 10 year follow up. SETTING: The town of Caerphilly, South Wales, and five adjacent villages. SUBJECTS: 918 men aged 45-59 at time of recruitment between 1979 and 1983. MAIN OUTCOME MEASURES: All deaths and deaths from coronary heart disease. RESULTS: Mortality risk was 50% lower in the group with high orgasmic frequency than in the group with low orgasmic frequency, with evidence of a dose-response relation across the groups. Age adjusted odds ratio for all cause mortality was 2.0 for the group with low frequency of orgasm (95% confidence interval 1.1 to 3.5, test for trend P = 0.02). With adjustment for risk factors this became 1.9 (1.0 to 3.4, test for trend P = 0.04). Death from coronary heart disease and from other causes showed similar associations with frequency of orgasm, although the gradient was most marked for deaths from coronary heart disease. Analysed in terms of actual frequency of orgasm, the odds ratio for total mortality associated with an increase in 100 orgasms per year was 0.64 (0.44 to 0.95). CONCLUSION: Sexual activity seems to have a protective effect on men's health.