Longer length of stay (LOS) in substance abuse treatment, a standard measure of treatment success, conflicts with pressures from managed care. To maintain LOS as an outcome, we identified, for four modalities, LOS categories such that program completion rates were relatively constant within category and differed among categories. We validated the cutoffs by showing that future utilization over a 2-year period by clients differed by category. Clients in the long-LOS category used the system in a way consistent with more successful treatment. Thus, rather than using increase in LOS as an outcome, one can use increase in the percentage of clients reaching the long-LOS category. Categories were developed and utilization analyzed for discharges from publicly funded Boston treatment programs between 1/92 and 12/94 from the following modalities: short-term residential (5,462 discharges), long-term residential (5,086 discharges), outpatient (13,656 discharges), and detox (19,965 discharges).