This study was performed retrospectively on 2,342 patients who were treated in the allergy department from 1985 to 1996. All patients had been skin prick tested with 40 common aeroallergens in Turkey. Allergen immunotherapy was given to 1,455 of them. Mean age of the patients was 25.9 (range 5 to 69). Fifty-five percent were males and 45.1% females. Forty percent had bronchial asthma and 60.2% had allergic rhinitis. Fifty-five percent of them had a family history of atopy. Sensitization to pollens was 59.7%, to house dust 20.5%, to molds 2%, to pollens and molds 2.9%, to pollens and house dust 11.5%, to molds and house dust 1.4%, and to pollens, molds and house dust 2%. The grass pollen sensitivity was threefold more common than that for trees, and fourfold more common than that for weed pollens. The diagnosis of bronchial asthma in the 5 to 9 age group was higher than in the other age groups (p < 0.005). The mold sensitization increased in parallel with age and it was the highest in 60 to 69 age group (p < 0.0001). There was no relationship between the allergens and sex, history of family atopy or blood group (p > 0.05) (except for house dust allergen). However, there was a relationship between month of birth (p < 0.005, p < 0.05, respectively) and birthplace (p < 0.001) with pollen and house dust allergen. House dust and molds were more common causes of bronchial asthma than pollens (p < 0.001, p < 0.01, respectively). In conclusion, the most common allergen was pollen in Turkey. In addition, atopic diseases are multifactorial, including such factors as genes and environment. Month and place of birth may influence early exposure and subsequent risk for allergy.