This study examined differences in demographics and substance-related problems in populations admitted to three substance abuse treatment settings--outpatient, intensive outpatient, and residential. The study tested whether interactions between client characteristics and type of setting predicted rates of 30-day retention and treatment completion. Three specific hypotheses were tested. The first was that more intense treatment settings would have client populations with more severe substance-related problems, compared to less intense settings. The second hypothesis was that drug and alcohol problems, employment problems, social stability, and psychiatric problems would demonstrate main effects in predicting retention or completion. The third hypothesis was that drug and alcohol problems, family/social problems, and psychiatric problems would interact with treatment setting such that clients with more severe problems would demonstrate lower retention and completion rates in outpatient settings, compared with similar clients in intensive outpatient (IOP) and residential settings. Participants were selected from a large administrative database containing records for people seeking publicly funded substance abuse treatment in Detroit, Michigan, between November 1995 and March 1999. Hypothesis 1 was supported. The level of substance-related problems in the residential population was generally higher than that of the IOP population, which was higher than the outpatient population. Hypothesis 2 was partially supported. More drug problems were associated with lower retention and completion rates, regardless of treatment setting. Hypothesis 3 was partially supported. The number of previous treatments and level of drug-related problems interacted with the treatment setting, such that clients with many previous treatments and more drug-related problems had lower completion rates in outpatient settings, relative to clients with many problems treated in more intensive settings. 2 figures, 4 tables, 31 references