Nutritional status and nutritional care have long been ignored among HIV/AIDS patients. Furthermore, in Mexico there is no information on potential factors favoring weight increase in such population. To assess the association between the time period since diagnosis, demographics and BMI in different categories of patients with HIV/AIDS in Monterrey, Mexico. In addition, to provide information on overweight/obesity prevalence and nutritional care referral. This was a cross-sectional study of HIV/AIDS positive patients receiving outpatient secondary care (n = 231). Nutritional care referral, time period since diagnosis and demographic data were obtained by interview. A standardized and registered dietitian collected anthropometrics measures. Binary multiple logistic regression was used to evaluate the association between increasing BMI categories and variables of interest. Mean patient age was 40.6 ± 11.2 years, 87% were male, 79.2% were economically active, 65% were single and 60% had less than a college education. The average time since diagnosis was 6.5 ± 5.4 years. Overweight and obesity prevalence were 35.8% and 12.5%, respectively. Only 18% of patients had ever been referred for nutritional care. The time period since diagnosis, the sum of skinfold measurements and the waist-to-hip ratio, were significantly predictive of the BMI category (normal/underweight vs. overweight/obese), when controlling for nutritional care referral and daily carbohydrate intake; age and marital status were not associated with BMI category. Identification of predisposing factors to overweight/obesity among HIV/AIDS patients constitutes a significant step for providing nutritional care, of the same importance as the load or CD4+ count, especially nowadays, with more common increased survival rates and consequently, longer lives with the disease.