OBJECTIVES: The objectives of this study were to (1) assess accuracy of hypoglycemia detection in children with type 1 diabetes and their parents, using personal digital assistant technology to collect glucose estimates and meter readings, (2) identify demographic, clinical, and psychological predictors of individual differences in accuracy, and (3) test whether poor hypoglycemia detection is a risk factor for severe hypoglycemia in children. METHODS: Sixty-one children aged 6 to 11 and their parents completed 70 trials, over 1 month, of a survey programmed on a personal digital assistant, which asked them to rate symptoms, estimate current blood glucose level, and then measure blood glucose level. For the subsequent 6 months, parents reported children's severe hypoglycemia episodes bimonthly. RESULTS: Both parents and children showed poor ability to recognize high or low blood glucose levels, making clinically significant errors as frequently as clinically accurate estimates. Parents failed to recognize >50% of readings <3 mmol/L (<55 mg/dL) and made potentially dangerous errors such as believing the blood glucose level was high when it was low 17% of the time. Children were significantly more accurate at recognizing their hypoglycemia but still failed to detect >40% of episodes. Higher depression scores for children related to lower accuracy. Children who were less accurate at detecting hypoglycemia subsequently experienced more severe hypoglycemia. CONCLUSIONS: Ability to recognize hypoglycemia is a significant problem for children with type 1 diabetes and their parents. For children, poor ability to detect low blood glucose levels may be a significant and underappreciated risk factor for severe hypoglycemia. More effort is needed to provide education and training designed to improve hypoglycemia detection in this population.