BACKGROUND: Severe hypoglycemia may increase the risk of a poor outcome in patients with type 2 diabetes assigned to an intensive glucose-lowering intervention. We analyzed data from a large study of intensive glucose lowering to explore the relationship between severe hypoglycemia and adverse clinical outcomes. METHODS: We examined the associations between severe hypoglycemia and the risks of macrovascular or microvascular events and death among 11,140 patients with type 2 diabetes, using Cox proportional-hazards models with adjustment for covariates measured at baseline and after randomization. RESULTS: During a median follow-up period of 5 years, 231 patients (2.1%) had at least one severe hypoglycemic episode; 150 had been assigned to intensive glucose control (2.7% of the 5571 patients in that group), and 81 had been assigned to standard glucose control (1.5% of the 5569 patients in that group). The median times from the onset of severe hypoglycemia to the first major macrovascular event, the first major microvascular event, and death were 1.56 years (interquartile range, 0.84 to 2.41), 0.99 years (interquartile range, 0.40 to 2.17), and 1.05 years (interquartile range, 0.34 to 2.41), respectively. During follow-up, severe hypoglycemia was associated with a significant increase in the adjusted risks of major macrovascular events (hazard ratio, 2.88; 95% confidence interval [CI], 2.01 to 4.12), major microvascular events (hazard ratio, 1.81; 95% CI, 1.19 to 2.74), death from a cardiovascular cause (hazard ratio, 2.68; 95% CI, 1.72 to 4.19), and death from any cause (hazard ratio, 2.69; 95% CI, 1.97 to 3.67) (P