Substance users' premorbid cognitive skills and abilities, assessed by their scores on standardized achievement tests (Iowa Tests of Basic Skills) during the fourth grade of elementary school, were examined as predictors of their problems at treatment intake and improvements with substance abuse treatment and case management over a 12-month follow-up period. Clients were assigned to four groups differing in the type of case management provided. Among 213 clients meeting criteria for the study, problems in several areas at treatment intake (assessed by the Addiction Severity Index) were milder for those with higher, relative to lower, premorbid cognitive abilities. Relationships of premorbid cognitive abilities to improvements at follow-ups were more prominent for clients who worked with case managers primarily via telecommunications than for clients who generally met with case managers at the substance abuse treatment or an independent agency, or who received only limited case management services from primary drug counselors. Thorough utilization of an interactive voice response system available to the telecommunications group might have placed demands on cognitive abilities that were less emphasized in the other groups. Alcohol differed markedly from other drugs in how improvements in problems were related to premorbid cognitive abilities among clients in the telecommunications group, and, to a lesser extent, among clients who generally met with case managers in person. Premorbid cognitive abilities should be considered when examining how outcomes are related to clients' characteristics and how maximally effective treatments can be selected based on clients' characteristics.