Background A certain weight gain occurs after obesity surgery compared to the lower weight usually observed between 18 and 24 months postsurgery. The objective of this study was to evaluate weight regain in patients submitted to gastric bypass over a 5-year follow-up period. Materials and Methods A longitudinal prospective study was conducted on 782 obese patients of both genders. Only patients with at least 2 years of surgery were included. The percentage of excess body mass index (BMI) loss at 24, 36, 48, and 60 months postsurgery was compared to the measurements obtained at 18 months after surgery. Surgical therapeutic failure was also evaluated. Results Percent excess BMI loss was significant up to 18 months postsurgery (p < 0.001), with a mean difference in BMI of 1.06 kg/m(2) compared to 12 months postsurgery. Percent BMI loss was no longer significant after 24 months, and weight regain became significant within 48 months after surgery (p < 0.01). Among the patients who presented weight regain, a mean 8% increase was observed within 60 months compared to the lowest weight obtained at 18 months after surgery. The percentage of surgical failure was higher in the superobese group at all times studied, reaching 18.8% at 48 months after surgery. Conclusion Weight regain was observed within 24 months after surgery in approximately 50% of patients. Both weight regain and surgical failure were higher in the superobese group. Studies in regard to metabolic and hormonal mechanisms underlying weight regain might elucidate the causes of this finding.186648651