Records from 1,228 consecutively admitted patients (74.5% male) to an inpatient detoxification unit in Barcelona between 1993 and 2006 were examined to determine factors associated with discharge against medical advice (AMA). 21.5% of admissions were discharged AMA. In multiple logistic regression and compared with patients who were medically discharged, those discharged AMA were younger, more likely to be dependent on heroin, other opiates, cocaine or psychostimulants, or to be experiencing reduction or elimination methadone maintenance therapy [reference category: alcohol]. The provision of assistance to clinicians in identifying the patients who are most at risk of leaving inpatient detoxification AMA will enhance their ability to motivate such patients to stay in treatment. ; Peer Reviewed ; Postprint (published version)