Findings revealed that most urine samples (84.1 percent) were negative. In the case of 17 prisoners, positive urine tests were associated with prescribed medications. Four positive tests resulted from drugs taken outside the prison. Three prisoners manipulated the urine sample, and 61 prisoners refused to provide urine samples. Urine samples of 54 prisoners (6.2 percent) were positive, and ingestion had occurred in prison. Cannabis was the most frequently misused drug among prisoners. Of the 874 inmates in the research sample, 259 had been assessed as drug misusers at the time of admission. Those classified as drug misusers had a higher proportion of positive findings, refusals, and prescribed medications than those classified as non-drug misusers. The highest proportion of positive findings and refusals was found in closed neighborhood prisons. 4 references and 4 tables