The prevalence of childhood asthma has increased markedly in many Western societies during recent decades. We wanted to study whether the incidence and severity of childhood asthma in Finland had changed during the time-period 1976-95. Hospital admission rates from 1976 to 1995 were obtained from the National Hospital Discharge Register and the individual intensive care unit (ICU) registers of the five university hospitals in Finland. The number and length of treatment periods for childhood asthma in all Finnish hospitals and at the ICUs of the five university hospitals were analyzed. The number of children receiving special reimbursement for asthma medication costs was obtained from the central register of the Social Insurance Institution. The data showed that during the time-period investigated, hospital admissions as a result of asthma had increased by 2.8-fold, but the mean length of hospital stay had more than halved (from 7.3 to 2.6 days). The increase in hospital admissions showed greatest significance in the 0-4-year age-group among both sexes (p <0.001). In contrast, a significant reduction in hospital admissions was found among the 10-14-year age-group (p <0.001). No discernible change in admission to ICUs was seen. During the same time-period, the number of children receiving special reimbursement for asthma medication costs increased 7.5-fold. Hence, a major increase has occurred in the number of children diagnosed with asthma that has not been paralleled by a proportionate increase in the number of hospital admissions. While the prevalence of mild and moderate asthma has increased, the occurrence of severe asthma has remained essentially unchanged.