The primary goal of this study was to identify factors associated with patients leaving a 3-day hospital detoxification unit against medical advice (AMA). Medical records of 302 patients who were admitted for alcohol or other drug withdrawal were reviewed. Variables examined were: demographics, reported history of drug use, urine toxicology at admission, medication received during the detoxification, and admission day. Data were analyzed using a case-control design. Logistic regression was used to identify independent predictors. We found that being younger, having a shorter history of cocaine abuse, being admitted on a Friday and being an opiate dependent patient treated with clonidine only during the detoxification, were significantly associated with leaving AMA. These findings may provide information that can help clinicians identify those patients who are most at risk for leaving AMA. This will in turn allow them the opportunity to initiate preventive measures to decrease unnecessary attrition and improve utilisation of treatment resources.