Fifty-six children with asthma, randomly selected from a hospital clinic, were followed prospectively for 15 years from a median age of 9-24 years of age. Four follow-ups were performed and included scoring of the frequency of wheezing, the need for medication, admissions to hospital, spirometry, skin prick tests and RAST to common inhaled allergens, and evaluation of living conditions. One patient died of asthma. The remaining 55 reported for all follow-ups. After the second follow-up at a median age of 13 years, all parameters of severity of asthma showed improvement, which was significant at the last follow-up when all subjects were more than 20 years of age. Only 16% of the subjects had been free from wheezing and medication the year prior to the last follow-up. Approximately 90% of the children had clinical allergies and positive allergy tests to pollens and danders and the majority of children retained both the allergies and the reactivity into adulthood. Reactivity to moulds and mites was less frequent (40% and 31%, respectively) and seemed to decrease in adulthood. Approximately 10% of the subjects developed neither clinical allergies nor reactivity in allergy tests. Children with atopic eczema usually retained their eczema as adults. Frequent wheezing and abnormal spirometry in childhood and early onset of asthma were associated with poorer outcome. The social prognosis was excellent.