To identify the clinical conditions associated with substantial time spent in hospital by children aged 1-14 years, records of children admitted to hospital in 1975, 1979, and 1984 were studied. Analysis was by linkage of abstracts of routine records of hospital inpatient care in six districts in southern England covered by the Oxford record linkage study. The total time spend in hospital in the acute specialties each year was calculated by summing the lengths of stay of all episodes of care for each child in each year. First, admissions with long median times in hospital per child admitted were identified. These included, notably, fracture of femur and, in the later years, leukaemia, other malignant neoplasms, and congenital disorders of metabolism. Second conditions were identified which accounted for large numbers of children with lengths of stay of five days or more. These included, in particular, congenital anomalies, asthma, and appendicitis. Third, conditions were identified which accounted for the largest numbers of bed days used. These included congenital anomalies, hypertrophy of tonsils and adenoids, asthma, otitis media, appendicitis, and head injury. Median time spent in hospital per child admitted declined for most conditions but increased for leukaemia, other malignant neoplasms, and congenital disorders of metabolism. Admission rates for children who spent five days or more in hospital each year declined for all common conditions except asthma which increased. Total numbers of beds used increased for asthma and otitis media but declined for all other common conditions.