Hypoglycemic episodes were studied in two large populations of prepubertal (332 subjects, aged 6-11 years) and adolescent (200 subjects, aged 12-18 years) diabetic children. We confirmed the majority of published data on incidence and causes of hypoglycemia and added some new information on the complex symptomatology and fear of hypoglycemia. Longer duration of IDDM induced a change in the symptomatology of hypoglycemia, consisting of a reduced occurrence of autonomic symptoms, namely tremor, and a parallel increased experience of neuroglycopenic symptoms, particularly drowsiness, difficulty in concentrating, and lack of coordination. The latter symptoms were found more frequently in patients with partial unawareness, more severe episodes and higher fear of hypoglycemia. These observations draw attention to the neuroglycopenic symptoms as important warning cues of hypoglycemia. We emphasized the necessity of observing the change in the frequency of symptoms experienced by patients, in particular autonomic and neuroglycopenic symptoms, in order to educate patients to preserve a normal awareness of hypoglycemia and prevent severe episodes.