Are longer stays in Veterans Health Administration (VHA) substance abuse residential rehabilitation treatment programs (SARRTPs) associated with better substance-related outcomes? To investigate, up to 50 new patients were randomly selected from each of 28 randomly selected programs (1,307 patients). The goal was to examine if patient and program average length of stay (ALOS) were associated with improvement on Addiction Severity Index (ASI) Alcohol and Drug composite scores in covariate-adjusted, multi-level regression models. Patients in programs with ALOS greater than 90 days tended to have more mental health treatment prior to the index episode and less severe substance-related symptoms, but more homelessness. At follow-up, programs longer than 90 days had the least improvement in the ASI Alcohol composite and significantly less improvement than programs with ALOSs of 15 to 30 and 31 to 45 days (both p < 0.05). Therefore, in VHA SARRTPs, ALOS greater than 90 days cannot be justified by the substance use disorder severity of the patients served or the magnitude of the clinical improvement observed.