Because of the high prevalence of marijuana smoking in Jamaica, it is important to know if this practice is associated with increased risk for STD infections. A national sample of 2 580 randomly selected Jamaicans, aged 15 to 49 years were administered a questionnaire to measure a number of health and behavioural variables. The results indicated that more persons who smoked marijuana before sex had a history of STD infections than non-marijuana smokers, the difference was significant among men (46% vs 26%, p < 0.001) but not among women (19% vs 8%, p = 0.09). There was no difference in age, however, more of the smokers were unmarried, poorly educated and unemployed than persons who did not smoke marijuana before sex. They were also more likely to engage in high risk sex behaviours and other risk taking behaviors than non-smokers. The results of multiple logistic regression analyses indicated that marijuana smoking before sex was an independent risk factor for STDs among men (Odds Ratio = 2.0, p = 0.04). Although it was not possible to determine if the association was causal, the increased risk for STDs among men who smoke marijuana before sex should be incorporated into the Jamaican STD/AIDS control programme by making special efforts to encourage condom use among marijuana smokers.