OBJECTIVE - To determine the incidence, predisposing factors, and costs of emergency treatment of severe hypoglycemia in people with type 1 and type 2 diabetes. RESEARCH DESIGN AND METHODS - Over a 12-month period, routinely collected datasets were analyzed in a population of 367,051 people, including 8,655 people with diabetes, to measure the incidence of severe hypoglycemia that required emergency assistance from Ninewells Hospital and Medical School (NHS) personnel including those in primary care, ambulance services, hospital accident and emergency departments, and inpatient care. Associated costs with these episodes were calculated. RESULTS - A total of 244 episodes of severe hypoglycemia were recorded in 160 patients, comprising 69 (7.1%) people with type 1 diabetes, 66 (7.3%) with type 2 diabetes treated with insulin, and 23 (0.8%) with type 2 diabetes treated with sulfonylurea tablets. Incidence rates were 11.5 and 11.8 events per 100 patient-years for type 1 and type 2 patients treated with insulin, respectively. Age, duration, and socioeconomic status were identified as risk factors for severe hypoglycemia. One in three cases were treated solely by the ambulance service with no other contact from health care professionals. The total estimated cost of emergency treatment of severe hypoglycemia was ≤£92,078 in one year. CONCLUSIONS - Hypoglycemia requiring emergency assistance from health service personnel is as common in people with type 2 diabetes treated with insulin as in people with type 1 diabetes. It is associated with considerable NHS resource use that has a significant economic and personal cost.