Background. Type 2 diabetes, hypertension and serum lipid abnormalities are common among obese people and they should improve with weight reduction. Aim: To study the outcome of these abnormalities after bariatric surgery in morbid obesity patients. Material and methods: Two hundred thirty two morbid obese patients subjected to gastric bypass, were evaluated in the preoperative period and every three months after surgeiy, during a minimum of 12 months. Clinical evolution, blood glucose, serum insulin, insulin resistance measured with the homeostasis model assessment (HOMA) and serum lipid levels were analyzed. Results: In the preoperative period, 17016 bad type 2 diabetes, 49016 bad abnormal serum lipid levels and 25% bad high blood pressure. Sixty six percent bad at least one of these abnormalities and 20% bad more than one. During follow up, body mass index decreased,from 44 to 29.3 kg/m(2). Total and HDL cholesterol, blood glucose and insulin resistance significantly decreased from the third month after surgery. Diabetes disappeared in 97% of diabetic subjects, blood pressure normalized in 53% of subjects with hypertension and serum lipid levels returned to normal in 88016 of subjects with dyslipidemia. Conclusions: Gastric bypass in morbid obese patients achieves a significant and important weight reduction that results in significant reductions in the frequency of diabetes, dyslipidemia and hypertension among operated obese subjects.