Data of the 1992-1993 Mexican Survey of Chronic Diseases in the Urban Adult Population were analyzed to investigate the effects of age and sex on the association between overweight and hypertension. Blood pressure, body weight, and height were measured in a group of 13,945 Mexicans aged 20 to 69 years living in towns and cities larger than 15,000 people. Hypertension was defined following the recommendations of the Joint National Committee for Detection, Evaluation, and Treatment of High Blood Pressure-V. Overweight was defined following the recommendations of the National Institutes of Health Consensus on Health and Obesity. The prevalence of types of hypertension was higher in men than in women, particularly in the groups of 20 to 39 years of age. Cross-classification of subjects according to the presence of hypertension and overweight confirmed the association between both variables. The odds ratio and 95% confidence intervals indicated that overweight was associated with systolic and diastolic hypertension and with isolated diastolic hypertension in women and, to a lesser extent, in men. This association was not found in the 60- to 69-year group in both sexes. Overweight did not show significant association with isolated systolic hypertension in both sexes. Results of a multiple logistic regression analysis of overweight on hypertension, controlling for age and sex, were consistent with these findings. It is suggested that other factors, independent of overweight, explain the observed gender-specific differences in the prevalence of hypertension in younger age groups. The hormonal environment of young women is one of the mentioned factors modifying the prevalence of hypertension in this group of the Mexican urban adult population.