Obesity is associated with increased morbidity and mortality. Intentional weight loss results in improvement of cardiovascular risk factors, but most observational studies suggest that weight reduction is associated with increased overall and cardiovascular mortality. No prospective intervention studies on mortality have earlier been reported in obese subjects. The prospective, controlled Swedish Obese Subjects Study enrolled obese subjects who either underwent bariatric surgery (n=2010) or were allocated to a contemporaneously matched, conventionally treated obese control group (n=2037). This review sums up effects on morbidity and mortality over an average of 10 years. The mean weight change of the control group was less than +/-2% over up to 15 years of weight recording. Maximum weight losses in the surgical subgroups were observed after 1-2 years. After 10 years, the weight losses from baseline were stabilized at 25, 16 and 14%, respectively. Bariatric surgery improved all traditional cardiovascular risk states except hypercholesterolemia over 10 years. There were 129 deaths in the control group compared with 101 in the surgery group. The unadjusted overall mortality was reduced by 23.7% (P=0.0419) in the surgery group (relative to controls), whereas the gender-, age- and risk factor-adjusted mortality reduction was 30.7% (P=0.0102). The most common causes of death were myocardial infarction (controls n=25, surgery n=13) and cancer (47/29). Bariatric surgery for severe obesity is associated with long-term weight loss, improved risk factors and decreased overall mortality.