To determine the dimensionality of items from the Composite International Diagnostic Interview—Substance Abuse Module (CIDI-SAM), responses to the 34 CIDI-SAM symptom items (17 each for alcohol and marijuana) obtained from 636 subjects who were alcohol and marijuana users from a representative community sample of young adults were subjected to factor analysis. Of the four factors extracted, one corresponded to alcohol dependence and another represented marijuana dependence. Alcohol and marijuana abuse items were not distinguished by substance, but rather by the domains of problems related to general substance abusing behavior. Within specific substances, dependence as measured by the CIDI-SAM appears to be a unidimensional construct. Conversely, abuse appears to be a multidimensional construct irrespective of the substance concerned.