Evaluations of drug treatment services are essential for the development and funding of future programs. This study tries to fill a void in the existing literature by comparing community and prison-based drug services in terms of a range of factors that are important in assessing drug treatment effectiveness. These factors are: (1) characteristics at treatment entry; (2) treatment services received from the recruitment agency; and (3) characteristics at the 8-month follow-up. These three areas equate with input, process, and outcome measures. Data were collected as part of the Drug Outcome Research in Scotland (DORIS) study. Over a period of approximately 8 months, 2 structured questionnaires were administered to 716 drug users. At the first interview, 487 respondents (68 percent) were beginning community drug treatment and 229 (32 percent) were starting prison drug treatment. Similar input and outcome measures were investigated. These related to life situation, drug use, relationships, and crime. Process measures investigated related to the kinds of treatment received from the recruitment agency and clients’ views of drug services. First, chi-square statistics were used to compare community treatment (CT) and prison treatment (PT) drug users in terms of their characteristics at input level, processes level, and outcome level. This showed how the two groups compared to each other at different levels of the treatment process. Secondly, McNemar tests for paired observations were used to compare input and outcome characteristics for the CT and PT groups to analyze how the two groups fared over time. Consistent with previous research, the findings provide evidence that, in the short term, drug treatments work. However, the clients in community based agencies experienced greater improvements than those clients of the prison-based services. The research shows that the prison services in Scotland are making efforts to assist their drug using inmates, but greater access to a wider range of prison drug treatments and efforts to improve prison clients’ perceptions of the help they receive are required. Tables, references