Urticaria is a common disease in children. In contrast to the ease of its diagnosis, etiologic factors are often difficult to determine. In order to study whether differences exist among various forms of urticaria in childhood and whether the patterns of different types of urticaria differ between adults and children, we extensively studied the possible causes of urticaria in children. Fifty-four children (23 girls and 31 boys; ages 1-19 years) with various forms of urticaria were included in the study. In all cases, questions about food allergies, food additive intolerance, drug intake, signs of infection, causes of physical urticaria, insect bites, and personal and family history of atopy were asked. Clinical characteristics of the disease, such as duration, recurrence, and associated angioedema and symptoms of anaphylaxis were also investigated. Detailed laboratory tests, including serologic, autoimmune, and allergic analyses, were conducted to reveal the probable etiologies of urticaria. Of the study patients, 68.5% and 31.5% were diagnosed as having acute and chronic urticaria, respectively. The patient group with chronic urticaria was older and included more boys than the acute group. In the acute urticaria group, infection was the most frequently documented cause (48.6%), followed by drugs (5.4%), and food allergies (2.7%), whereas in chronic urticaria, physical factors were the leading cause (52.94%). The most frequently documented infection was urinary tract infection, followed by serologically determined infections of Chlamydia pneumoniae and Helicobacter pylori. In this study we found indications that infections were frequently associated with urticaria, which suggests that urticaria management should include a survey of certain infectious agents in addition to a detailed history.