The aim was to evaluate the differences of mortality among asthma and COPD patients on the basis of the first period of hospitalization of these diseases. A total of 576,916 treatment periods for asthma and COPD between 1972 and 1992 were identified in the discharge register maintained by the National Research and Development Centre for Welfare and Health. Patients aged 50-54 years first treated in hospital in 1977 or later were analysed. There were 6655 new asthma patients of this age, 2727 new COPD patients and 701 new patients in a mixed group (with both diagnoses). Mortality up to the end of 1993 was analysed based on mortality and cause of death data provided by the Central Statistical Office of Finland. Estimated cumulative survival after 10 yr was higher among the asthma patients (83.5% for men and 93.2% for women) and lower among the COPD patients (60.1% and 78.0%) and in the mixed group (62.5% and 74.4%). The main cause of death among the asthmatics was asthma in 12.1% of cases, that among the COPD patients was COPD in 22.1% of cases and that in the mixed group was one or other of these diseases in 39.1% of cases. The prognosis for COPD patients aged 50-54 years requiring hospital treatment is poor. Combination of the data available from the cause of death and hospital discharge registers indicates that obstructive pulmonary diseases may well be of more significance from a public health point of view than the mortality statistics would lead us to believe. The very first hospitalization for COPD calls for a thorough evaluation of the prospects for active treatment and prevention.