There is widespread concern about the use and abuse of alcohol and other drugs by adolescents and young adults. It has yet to be determined whether drug use in itself is invariably associated with disruptive or problem use of drugs. Additionally, drug use may vary by frequency and quantity of ingestion which may be differentially related to disruptive or problem use of drugs. To explore these issues, data were obtained from 739 young adults as part of an 8-year longitudinal study of drug use and abuse. A multitrait/multimethod approach with latent variable models was used to separate use factors of particular drugs (alcohol, cannabis, hard drugs, cocaine) from latent constructs of general drug use frequency, quantity, disruptive drug use, and problem drug use. Self-reported frequency of use measures were based on 7-point rating scales that ranged from "no use" to "more than once a day." Twenty-one different substances were assessed; there were two quantity of drug use measures. Disruptive and problem drug use were also assessed. Regression paths between Drug Use Frequency and Disruptive and Subjective Problem Drug Use were not significant; however, the paths between Drug Use Quantity and Subjective Problem Use were significant at greater than the .01 level. These results tend to suggest that the quantity of substances used is more important in the etiology of problem and disruptive use of drugs than is frequency of use for young adults. (NB)