Management of a first attack of acute urticaria in children is dependent on the etiology of the disease. Knowledge of the various etiologies of urticaria will help primary physicians to perform appropriate clinical assessments. In this study, we analyzed the etiologies and their prevalence in first-attack acute urticaria in infants, children and adolescents in central Taiwan. Methods: This was a retrospective study of 953 children who were admitted to the emergency department (ED) with a first attack of acute urticaria from January 2000 to December 2006. All patients were followed in the ED or outpatient department until their symptoms subsided. Patient demographics and detailed etiologies of the first attack of acute urticaria were analyzed. Furthermore, the prevalence of various etiologies in different age groups, as well as the etiologic trends of acute urticaria in children during the previous 7 years, was determined. Results: The most common etiologies of a first attack of acute urticaria in children were various infections (48.4%), foods (23.5%), idiopathic causes (13.2%), and medications (11.5%). Among the three major etiologies above, upper respiratory tract infections (nasopharyngitis), seafood (shrimp) and nonsteroidal anti-inflammatory drugs (ibuprofen) were the most frequent causes. Moreover, the etiologies differed significantly with patient age (p < 0.001). Overall, infections were the major cause in infants (56.5%), whereas food (36.6%) and medications (26.8%) were the most common etiologies in adolescents. The prevalence of various infections dropped as the age of the children increased (56.5% in infants, 51.2% in preschool-aged children, 42.1% in school-aged children and 17.1% in adolescents). The etiologies of foods and medications were more prevalent in adolescents than in younger children. Conclusion: Detailed etiologies of first-attack urticaria in children in central Taiwan were analyzed. Most importantly, we found that there was a decrease in the prevalence of various infections as causative factors as the age of the children increased. The etiologies of foods and medications were more prevalent in adolescents than in younger children.