Objective: To evaluate effect on comorbid disease and weight loss 5 years after Roux-en-Y gastric bypass (RYGB) surgery for morbid obesity in a large nationwide cohort. Background: The number patients having surgical procedures to treat obesity and obesity-related disease are increasing. Yet, population-based, long-term outcome studies are few. Methods: Data on 26,119 individuals [75.8% women, 41.0 years, and body mass index (BMI) 42.8 kg/m(2)] undergoing primary RYGB between May 1, 2007 and June 30, 2012, were collected from 2 Swedish quality registries: Scandinavian Obesity Surgery Registry and the Prescribed Drug Registry. Weight, remission of type 2 diabetes mellitus, hypertension, dyslipidemia, depression, and sleep apnea, and changes in corresponding laboratory data were studied. Five-year follow-up was 100% (9774 eligible individuals) for comorbid diseases. Results: BMI decreased from 42.8 +/- 5.5 to 31.2 +/- 5.5 kg/m(2) at 5 years, corresponding to 27.7% reduction in total body weight. Prevalence of type 2 diabetes mellitus (15.5%-5.9%), hypertension (29.7%-19.5%), dyslipidemia (14.0%-6.8%), and sleep apnea (9.6%-2.6%) was reduced. Greater weight loss was a positive prognostic factor, whereas increasing age or BMI at baseline was a negative prognostic factor for remission. The use of antidepressants increased (24.1%-27.5%). Laboratory status was improved, for example, fasting glucose and glycated hemoglobin decreased from 6.1 to 5.4 mmol/mol and 41.8% to 37.7%, respectively. Conclusions: In this nationwide study, gastric bypass resulted in large improvements in obesity-related comorbid disease and sustained weight loss over a 5-year period. The increased use of antidepressants warrants further investigation.