Abstract Using structured psychiatric interviews, 73 attention deficit disorder (ADD) patients, 26 psychiatric control patients, 26 normal controls, and all available first degree relatives of these index children were examined. ADD subgroups with and without comorbid psychiatric disorders did not differ on rates of specific ADD symptoms. The construct of ADD is internally consistent as measured by Cronbach's alpha. The diagnostic efficiency of individual items is presented. A receiver operating characteristic-based procedure is used to create an ADD diagnostic algorithm that is more efficient in discriminating ADD children from controls than the DSM-III-based clinical diagnosis. Cross-validation with family study data shows this procedure to be superior to the procedure used for the DSM-III-R diagnosis. The results show that proponents of conditional probability and receiver operating characteristic analyses are correct in asserting that the examination of symptom combinations may result in better diagnostic algorithms.