The prevalence of allergic diseases such as asthma and allergic rhinitis is high in general population and aeroallergens are the most common allergens that cause air way inflammation.The aim of this study was an evaluation of clinical and laboratory findings in allergic patients and identification of the most common aeroallergen in these patients.A cross-sectional retrospective study was conducted on 226 allergic patients who were referred to allergic clinic of Karaj city, and skin prick test response to aeroallergens were studied. The most common risk factors in these patients were total IgE more than 100 IU/ml and a positive family history of atopy. Skin prick testing results showed that the most common aeroallergens were: herbacee II (62%), sycamore (57%), chenopodium (53%), tree mix (50%), herbacee III (47%), grass (43%), ash (40%), herbacee I (37%), cedar (27%), cockroach (25%), and mite D.P (19%), D.F (18%).High prevalence of skin reactivity to weeds (chenopodium and herbacee) and sycamore indicates variation in the prevalence of aeroallergen reactivity in different regions with different climates.