Seventy-five drug addicts who completed an opiate detoxification program were compared with 75 addicts who dropped out prematurely on 14 variables. Results showed that patients were more likely to complete detox when the number of staff absences and primary therapist absences increased, when more patients were admitted during their hospitalization, and if they were prescribed methadone. A discriminant function analysis successfully classified 88% of the sample into stay/ leave categories. The results were cross-validated on an independent sample of 25 completers and 25 dropouts, resulting in 75% classification accuracy. Primary drug of abuse (heroin/Talwin) was not a factor on any measure. Results indicate that treatment dropout among drug addicts is based more on situational interactionism than on individual determinism.