Background: Urticaria is a common skin disease characterized by transient and itchy swelling. The spectrum of etiologic factors in urticaria is very wide and contains external factors such as drugs, foods and internal diseases such as infections, SLE, hormonal factors and even lymphoma. Objective: To determine different kinds of urticaria and different etiologic and prevocational factors in patients with urticaria. Patients and Methods: This descriptive study was carried on 120 patients with urticaria referred to Razi Hospital in Tehran in year 1376. They were evaluated in two groups: Acute and chronic urticaria, duration of 6 weeks was the limit between them. Results: About 30% of patients had acute urticaria and causes were determined in 58% of them. Upper respiratory tract infections, drugs and foods were the most common etiologic factors. In only 22% of patients with chronic urticaria, the causes were found, which included infections (Sinusitis, hepatitis B, intestinal parasitic infections), drugs (NSAIDs and Codeine) and food. Fifty percent of these patients had common urticaria, 22% of them were affected with one of the physical urticarias and in 22% of them a combination of two or more kinds of urticaria were founded. Conclusion: The most important factor in determining the cause and provocation of urticaria are taking detailed history and performing thorough clinical examination. Paraclinical studies had a little role in determining etiology of urticaria.