Objective: The implementation of intensive insulin therapy in the intensive care unit is accompanied by an increase in hypoglycemia. We studied the relation between hypoglycemia on intensive care unit mortality, because the evidence on this subject is conflicting. Design: Retrospective database cohort study. Setting: An 18-bed medical/surgical intensive care unit in a teaching hospital (Onze Lieve Vrouwe Gasthuis Hospital, Amsterdam, The Netherlands). Patients: A total of 5961 patients admitted to from 2004 to 2007 were analyzed. Readmissions and patients with a withholding care policy or with hypoglycemia on the first glucose measurement were excluded. Patients were treated with a computerized insulin algorithm (target glucose range, 72-126 mg/dL). Interventions: None. Measurements and Main Results: All first episodes of hypoglycemia (glucose ≤45 mg/dL) were derived from 154,015 glucose values. Using Poisson regression, the incidence rates for intensive care unit death and incidence rate ratio comparing exposure and nonexposure to hypoglycemia were calculated. Patients were considered to be exposed to hypoglycemia from the event until the end of intensive care unit admittance. We corrected for severity of disease using the daily Sequential Organ Failure Assessment score. Age, sex, cardiothoracic surgery, sepsis, and diabetes mellitus were also included as possible confounders. Two hundred eighty-eight (4.8%) patients experienced at least one episode of hypoglycemia. Median age was 68 yrs (range, 58-75 yrs), 66% were male, and 6.4% died in the intensive care unit. The incidence rate of death in patients exposed to hypoglycemia was 40 per 1000 intensive care unit days compared with 17 per 1000 intensive care unit days in patients without exposure. The adjusted incidence rate ratio for intensive care unit death was 2.1 (95% confidence interval, 1.6-2.8; p