This study compares the characteristics of two groups of probationers ordered to jail-based substance-abuse treatment as an intermediate sanction. It further reviews rearrest and probation failure outcomes of the two groups, along with the demographic, clinical, and criminal factors associated with those outcomes. Probationers jailed for probation violations had higher rates of rearrest and probation failure in the first year after program completion compared to probationers jailed immediately after conviction. Factors associated with rearrest and probation failure varied widely between the two outcomes and between the two probation groups. This study concludes that jail-based substance-abuse treatment should be an option in a range of intermediate sanctions and treatments for selected probationers. (Contains 4 tables.)