The national prevalence of asthma, hay fever and eczema, employing the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire, was determined during 1995 in 3148 Junior Certificate secondary school children aged 13-14 years throughout the Republic of Ireland. The prevalence values for asthma, hay fever and eczema were 15.2%, 24.8% and 9.4% respectively. Although 5.4% reported having both asthma and hay fever, combinations of the other allergic conditions were less than 2%. Sex difference in prevalence rates for the various conditions occurred with asthma prevalence being higher for males, eczema in females, but hay fever was almost equally reported between males and females. This data documents the prevalence of teenage asthma with associated allergic conditions in the Republic of Ireland and will allow for present and future comparisons of these conditions with other countries world-wide using the ISAAC protocol.