Over the period 1986-88, 261 infants and children, with a mean age of six months, were admitted to Christchurch Hospital with acute bronchiolitis. There was a marked seasonal pattern, with peak admission periods occurring during winter and spring. Two hundred and two children (77%) had a nasopharyngeal aspirate performed for respiratory virus identification. Respiratory syncitial virus was identified in 113 (56%) of those who had viral studies performed. Using a score of severity, 150 (57%) of the children had a mild disease, 47 (18%) moderate, while 64 (25%) had a severe or very severe illness. The median stay in hospital was two days. No deaths occurred during the study period, although six infants required assisted ventilation.