Background: Eczema is one of the most widely spread inflammatory skin disorders contact dermatitis is an eczematous dermatitis that is produced as a result of contact with a substance in the environment. The substance can act as an irritant or allergen. Every country has allergen particular to itself. Objective: Determining the frequency of skin allergens in patients with contact dermatitis in Tehran. Patients and Methods: In this cross-sectional descriptive study, all the data about the patients with chronic contact dermatitis who were visited in a dermatology clinic in Tehran from the year 1993 to 2003 and patch tested with 23 allergens of European standard series (ESS) were analyzed. Results: In this study 222 patients were surveyed. The mean age of the patients was 33.5 years (SD=13.8). 66.5% of the patients were female. The most common site of involvement (49%) was their hands. The mean duration of the disease was 54 months (SD=62). Clinical diagnosis included: 59% allergic contact dermatitis, 24% irritant dermatitis, 10% atopic dermatitis, and 7% other types of dermatitis. 145 (65.3%) of them had at least one positive reaction. The most common allergens were: Nickle sulfate 22.6%, cobalt chloride 14.5%, and fragrance mix 13.6%. Conclusion: Nickel was the most common contact allergen among the patients surveyed.