Atopic dermatitis is a chronic inflammatory skin disorder, for which it is difficult to obtain epidemiologic findings. In a previous study, we suggested the following diagnostic criteria for atopic dermatitis in the adult Thai population: visible flexural dermatitis, a history of flexural dermatitis, a rash of more than six months duration and visible dry skin. However these criteria were not validated against physicians' diagnoses. In the present study, we validated these diagnostic criteria for atopic dermatitis in the Thai population in a clinical setting. A case-controlled study was performed on a total of 259 patients; 33 subjects with active atopic dermatitis, 26 with inactive atopic dermatitis, 100 controls presenting with an inflammatory skin disorder other than atopic dermatitis and 100 controls without any skin disease. Each patient was examined according to the above criteria. Sensitivity, specificity, relative value, positive predictive value, and negative predictive value were calculated for each individual criterion and for composite criteria. Our data confirmed that in order to achieve satisfactory sensitivity and specificity for diagnosing atopic dermatitis in Thai people older than 13 years, a patient must have a history of flexural dermatitis plus two or more of the other mentioned criteria.