Two structured interviews, the Schedule for Affective Disorders and Schizophrenia-Lifetime (SADS-L) and the National Institute of Mental Health Diagnostic Interview Schedule (NIMH-DIS), were compared as methods of reducing information variance in the diagnostic process. Forty-two patients newly admitted to an alcohol treatment unit were randomly selected and were independently interviewed using the SADS-L and NIMH-DIS. The order of the interviews was random and they were separated by three to four days. Interrater reliability for each interview schedule was calculated using the kappa statistic and was found to be high. The degree of diagnostic concordance between the two interview schedules for several diagnostic categories was also found to be high.