The occurrence of severe and mild hypoglycaemic attacks and their symptoms and signs were studied in 92 insulin-dependent diabetic children, 7-18 years old. A questionnaire was distributed to all families and they were interviewed by an experienced nurse. Severe attacks, for which the help of an adult was needed, were reported by 44% of the children during a 12-month period. Thirty-seven per cent of the attacks occurred in the mornings, most often attributed to extra physical exercise, but equally often without any obvious cause. They were more common in children with strict blood glucose control measured as HbA1c. Fast-acting carbohydrates, given by parents, relieved the attack in most children, but 15% needed a glucagon injection and 12% intravenous glucose. In all, 16% were admitted to hospital. Mild events occurred in 97% of the children, at least once per week in 53% of the children, and were not related to blood glucose control. They were often attributed to extra physical exercise and occurred mainly between breakfast and lunch. Initial symptoms were tremor and hunger; during the whole event tremor and sweating were most common. Parents noted pallor as the most common sign. The frequency of severe or mild attacks could not be correlated to the age of the child, duration of diabetes, daily dose or number of insulin injections.