There is evidence to suggest that the prevalence of asthma is increasing internationally. The reasons for the increase are unclear as asthma is caused by an interplay of genetic and environmental factors. As asthma is not a notifiable disease, there are no precise statistics available on the number of people with the condition in Ireland. For the most serious asthmatic reactions requiring hospitalisation, data are available from hospital in-patient inquiry system. The data avail able in respect of males and females for 1998 is set out in the following table. These figures are based on principal diagnosis and include day cases and in-patients. It should be noted that information is not available from private hospitals and that a person attending hospital several times in a given year is counted separately in the statistics for each visit.