To assess the prevalence of allergic diseases and atopy in adults, a two-step population-based epidemiological study was undertaken in Ankara, the capital city of Turkey. In step 1, a screening questionnaire adapted from the European Community Respiratory Health Survey (ECRHS) was applied in a cross-sectional manner. In step 2, a nested case-controlled design study was conducted and subjects were evaluated in the clinical setting for history, physical examination, skin prick tests (SPTs), and serum total IgE and phadiotop measurements. According to the results, self-reported current asthma prevalence in step 1 was lower compared with that in step 2 (3% vs. 7%, p < 0.05). The prevalences of food and drug allergy were 6.2% and 3.9%, respectively, in step 1, but were not demonstrated in any of the subjects in step 2. The overall prevalence of atopy was 25% after step 2 evaluation. In conclusion, allergic disorders are not uncommon in our adult population; however, sole application of a screening questionnaire appeared to be ineffective in revealing the accurate figures of asthma, and food or drug allergy.