Overweight or obese adults have demonstrated a survival advantage compared with leaner adults in several population-based samples. This counterintuitive association has been termed the obesity paradox. Evidence for an obesity paradox among persons with diabetes has been less consistent. In the present review, we identified 18 longitudinal studies conducted in cohort studies, patient registries and clinical trial populations that tested the associations between obesity and survival in patients with diabetes. The majority of these studies reported that mortality was lowest in overweight and obese persons, and that leaner adults had the highest relative total and cardiovascular mortality. Some of these studies observed the patterns most strongly in older (age > 65 years) adults. To date, little research has been conducted to identify mechanisms that could explain elevated mortality in leaner adults with diabetes, or to identify strategies for diabetes management or mitigation of elevated mortality risk.