The United Kingdom Working Party diagnostic criteria for atopic dermatitis have been characterized in infants and children; however, the need for visual confirmation of flexural dermatitis by a trained investigator limits their use in large epidemiologic studies. We have administered the complete United Kingdom Working Party criteria in a postal questionnaire format to the mothers of year old infants and determined the concordance between mothers' and trained investigator's reports of visual flexural dermatitis. Based on mothers' responses to the questionnaire, 59 infants with atopic dermatitis and 59 controls were identified. In subsequent home interviews conducted by a trained investigator, the United Kingdom criteria questions were repeated and sites of current visible dermatitis were identified by mothers and the investigator as per United Kingdom Working Party protocol. Agreement between the mothers' postal and home interview responses was high: kappa= 0.75-0.94 for individual criteria; kappa= 0.93 for diagnosed atopic dermatitis. Agreement between the mothers' and investigator's observations of visible flexural dermatitis was high for all sites: kappa= 0.88-1.0. The results demonstrate that mothers are able to apply the United Kingdom criteria and accurately report visible flexural dermatitis in their year old infants. The postal application of the United Kingdom Working Party's diagnostic criteria for atopic dermatitis in year old infants appears to be a practical, reliable, epidemiologic tool in the investigation of atopic dermatitis with results comparable with formal application of the criteria by a trained investigator.