Symptomatic episodes of documented hypoglycaemia were characterized with the aid of a 3-month diary in a single-centre, unselected group of 161 children and adolescents with Type 1 diabetes mellitus, treated mainly (81%) with multiple-dose insulin therapy. Patients and families were asked to write in the diary all the symptomatic episodes in which blood glucose concentration proved to be less than or equal to 3 mmol l(-1) before treatment. Of the patients, 83 (52%) had a total of 287 hypoglycaemic episodes (0.6 attack per month per patient). The majority of the attacks, 221 (77%), were mild (patients greater than or equal to 6 years able to treat themselves). Only two attacks were severe, resulting in coma and/or convulsion. The most common dominant symptoms were weakness (29%), tremor (20%), hunger (14%), and drowsiness (12%). Of all the dominant symptoms, 39% were classified as autonomic, 20% neuroglycopenic, and 41% non-specific, In children under 6 years, autonomic symptoms were less common than in adolescents 15 years or over (34% vs 57%, p = 0.01). In conclusion, the incidence of documented symptomatic hypoglycaemia was low. The symptoms were more often neuroglycopenic or non-specific than autonomic, especially in young children. (C) 1998 John Wiley & Sons, Ltd.