OBJECTIVE: To determine the prevalence of obesity and its association to different variables in urban and rural older Mexican populations. METHODS AND PROCEDURES: A cross-sectional study of three different Mexican communities. A total of 121 men and 223 women 60 years and older and 93 men and 180 women aged 35 to 59 years old were selected randomly for inclusion in the survey. A personal interview assessed demographic information, personal medical history and functional status and a 24-hour diet recall was obtained. The physical examination included anthropometric and blood pressure measurements. A fasting blood sample was obtained for measurements of lipids, insulin and glucose. RESULTS: Obesity was highly prevalent in women, in individuals from the urban communities and diminished with advancing age. A BMI > or =30 kg/m2 was observed in 23.6% younger vs. 15.6% older adult men (p=0.21) and 28.4% younger vs. 19.7% older adult women (p = 0.06). The association of obesity with other variables was estimated using a stepwise multivariate logistic regression, increased insulin levels [Odds Ratio (OR) 1.68, p=0.006] and living in an urban area (OR 5.90, p<0.007) were variables independently associated to obesity in adult older individuals. In the younger adults, obesity was associated with hypertension (OR 2.74, p<0.0009), higher insulin levels (OR 1.31, p<0.03) and central adiposity (OR 2.97, p = 0.05), these relationship were not observed with gender, distribution of food or alcohol intake or other coronary risk factors. CONCLUSIONS: The present survey confirms the high prevalence of obesity in the Mexican urban population that declines with advanced age. Studies in elderly population must consider the bias produced by increased early mortality in those individuals with a more unfavorable risk profile.