The present research was conducted to examine the effects of pretreatment psychiatric status and tieatment duration on improvement following drug abuse rehabilitation. Percent improvement from admission to 6-month follow-up was measured on three criteria: drug use, employment, and criminality. Analyses of the total samples in both the Therapeutic Community (TC) and Methadone Maintenance (MM) programs indicated some quantitative differences between the two modalities but all measures showed a strong and positive relation between treatment duration and percent improvement. When patients in the two program samples were divided, on the basis of admission psychiatric status, into LOW,MID, and HIGH severity groups, different findings emerged. LOW severity patients in both programs showed the greatest absolute levels of improvement in most measures, more improvement at shorter treatment durations, and less additional improvement at longer treatment durations. MID severity patients in both programs showed the most dramatic effects of treatment duration, with generally large improvements in all criteria at greater treatment lengths. Qualitatively different results were seen between the treatment programs for