The occurrence of allergic diseases in preschool children was studied on the basis of a questionnaire sent to the parents of 5,408 kindergarten students, 3 to 6 years of age, in Taichung City. The overall response rate was 81% and included 2311 (52.8%) boys and 2062 (47.2%) girls. Allergic diseases had been recognized in 34.6% of the children. The cumulative (lifetime) prevalence of bronchial asthma (BA), allergic rhinitis (AR), atopic eczema (AE), and urticaria were 9.4%, 26.4%, 6.6% and 6.8%, respectively. The current (past 12 months) prevalence of BA, AR, and AE was 6.7%, 14.8%, and 3.5%, respectively. BA and AR occurred more frequently in boys than in girls (P < 0.001); no significant difference was found between boys and girls in AE (P = 0.328). There were statistically significant relationships between positive family history and BA, AR and AE (P < 0.001). In conclusion, allergic diseases constitutes an important health problem for pre-school students in Taichung City.