Purposes: This study's aim was to determine the predictive factors of the duration of first-attack acute urticaria in children. Basic Procedures: The sample included 1075 children admitted to the emergency department with first-attack acute urticaria. Variables comprising the clinical features and past histories of children with duration of disease of 3 days or less, 4 to 7 days, 8 to 14 days, and 15 days or more were compared to determine the predictors of duration of acute urticaria. Main Findings: Age, various etiologies, clinical presentations, coexistent pyrexia or angioedema, and personal histories of allergic diseases were significant factors (all P <.05). Among allergic diseases, atopic dermatitis was the most significant predictor of duration of acute urticaria, and those with multiple allergic diseases had longer durations of urticaria (both P <.05). Oral plus injection forms of antihistamine or steroid were related to shorter duration of disease (P <.05). Principal Conclusions: Etiologies and personal allergy history may be the most important predictors of the duration of a first attack of acute urticaria.