In order to qualify as a case of atopic dermatitis, we propose that an individual must have an itchy skin condition plus three or more of the following: history of flexural involvement, a history of asthma/hay fever, a history of a generalized dry skin, onset of rash under the age of 2 years, or visible flexural dermatitis. When tested in an independent sample of 200 consecutive dermatology outpatients of all ages, this arrangement of the diagnostic criteria achieved 69% sensitivity and 96% specificity when validated against physician's diagnosis. Based on the findings of this first exercise, minor modifications in the wording of the criteria were undertaken, and these were tested on a sample of 114 consecutive children attending out-patient paediatric dermatology clinics. Overall discrimination improved, with a sensitivity of 85% and specificity of 96%. The simplified criteria are easy to use, take under 2 min per patient to ascertain, and do not require subjects to undress. These two independent validation studies suggest that the newly proposed criteria for atopic dermatitis perform reasonably well in hospital out-patient patients. Further validation in community settings and in developing countries is needed.