The purpose of this study is to determine if a significant relationship exists between the sociodemographics, substance use characteristics, criminal history, and completion of substance abuse treatment. In this study, 115 individuals being monitored for substance abuse treatment on probation at the Probation and Help Center under the Republic of Turkey's Ministry of Justice's Chief Public Prosecutor's Office of Istanbul were included successively between the dates of April 2008 and April 2009. During a 24-week follow-up, individuals whose urine analyses were clean 6 times consecutively were considered to have completed the treatment successfully. To determine the effect of sociodemographic factors and substance use characteristics on treatment completion, a semistructured sociodemographic data survey was used. Also, the participants' criminal records were examined. Atotal of 115 people participated in the study. One hundred ten (95.7%) of them were male. Sixty-eight (59.1%) of the participants had completed treatment. Age group, education level, age of onset for substance use, number of substances used, employment status, and criminal records showed a significant difference between treatment completers and noncompleters. When a logistic regression analysis was done, only number of substances used and criminal record (other than drug possession) were significantly different for the 2 groups. The current treatment program for polysubstance users and individuals with a criminal record is insufficient. It is necessary that treatment systems be developed so they can be beneficial for these types of patients.