OBJECTIVE To describe the impact of obesity on the nutritional status of Mexican pregnant women. METHODS In a group of 155 pregnant women we assessed weight gain, nutrient intake before and during pregnancy, food patterns, and anemia prevalence. RESULTS Weight gain in obese women during the third trimester was lower (2.2 kg) than in normal weight women (8.7 kg), and 22% of them lost weight. Obese women tend to consume less energy per kilogram of body weight. Some unhealthy food patterns were observed, including high saturated fat and cholesterol intake and low fruit and vegetable consumption. Anemia was present in 28% of women. Some micronutrient deficiencies were observed (zinc, folate, iron and other vitamins). CONCLUSIONS Studies to assess healthy weight gain among obese Mexican pregnant women are needed. Nutrition education should be done to promote healthy eating patterns in this population.