The purpose of this study was to examine possible seasonal variations in relations between hospital treatment periods and in deaths (asthma-related and other) among adult asthmatics. Out of a total of 364,871 asthma-induced hospitalization periods (diagnosis No. 493, International Classification of Diseases) recorded in the hospital discharge register maintained by the National Research and Development Centre for Welfare and Health during 1972-1992, all of those applying to persons aged >24 yrs during 1987-1992 were analysed here. The discharge file was linked to the register of deaths on the basis of the patients' social security numbers in order to analyse all deaths among the same patients during 1987-1993. A total of 81,243 asthma-related treatment periods were analysed. The monthly variation in the number of such periods showed a peak in January (18.2% above the mean number of monthly deaths in the study period) and a trough in July (26.1% below the mean). Of the 7,622 hospitalized asthmatics who died during the period examined here, 1,274 died of obstructive pulmonary diseases, with asthma as the primary cause in 489 cases. The majority of the deaths were caused by cardiovascular diseases. Mortality was highest in January (+14.7%) and lowest in August (-12.3%). The similarity in the seasonal variation observed between the treatment periods and deaths recorded for adult asthmatics may be taken to indicate a genuine need for treatment.