This paper examines the null hypothesis that there is no difference between male and female drug abuse clients in length of time spent in treatment and successful outcome of that treatment. The hypothesis is tested by means of multiple classification analysis on a random sample of 20,264 clients who were discharged from federally-funded drug abuse programs in 1975. Upon controlling for the effects of demographic client characteristics, treatment history, and drug usage, the authors conclude that the null hypothesis is sustained. Small differences are apparent, especially with respect to the length of time spent by clients in drug-free modality and day-care environment and in detoxification modality and hospital environment, and with respect to treatment success for clients in drug-free environment and hospital environment. However, these differences are not sufficient to warrant a rejection of the null hypothesis.