We studied the prognosis of childhood asthma in a cohort of 406 children 8 to 12 yr of age when enrolled. Subjects were followed for a mean of 14.8 yr after their initial evaluation, with a follow-up rate of 86%. The mean age at follow-up was 24.7 yr. We assessed the predictive value of sex and various childhood variables on the outcome of symptoms and medication use in adulthood. Although only 19% of subjects were still under a physician's supervision at the time of follow-up, 76% had respiratory symptoms, 32% used maintenance medication, and 22% used medication intermittently. The incidence of cigarette smoking was disturbingly high (33%). In adulthood, women were more likely than men to have symptoms (85 versus 72%, respectively). The childhood symptom severity and the childhood degree of bronchial responsiveness in combination with a low %FEV1 were also related to the outcome of asthma in adulthood. The high prevalence of symptoms in adults at follow-up coupled with the low rate of physician supervision and medication usage suggest that more aggressive treatment may be indicated in asthmatic children.