Four methods (self-reported rating, self-reported intake, peer-reported rating, peer-reported intake) and multiple analytical criteria were employed to assess the construct validity of reports of three types of substance use (alcohol, marijuana, and cigarettes) in a study of 194 college students who were members of friendship pairs. The resulting multitrait-multimethod matrix was analyzed in the traditional fashion as well as with confirmatory factor analysis. Convergent and discriminant validity for the three substance use traits were quite adequate, although the validity of one measure (the peer-reported intake measure of alcohol use) may be considered inadequate according to some criteria. This study demonstrates the usefulness of multimethod assessment and confirmatory factor analysis for research on construct validity and for derivation of more accurate measures of drug use.