This hypothesis-generating study attempts to identify patient characteristics predicting the successful outcome of methadone maintenance in the treatment of narcotic addiction. The sociodemographic characteristics as well as the general emotional health of 51 addicted individuals in Montreal were studied at entry into the program and are correlated with success one year after entry. The success of the Montreal program, defined as retention in the program and urine samples negative for opiates, is comparable to results reported from many North American clinics. A history of foster care before age 15 is the only characteristic significantly correlated with both retention and negative urines. Emotional health, previous treatment experiences, job status, and level of education do not correlate with success. All addicted individuals applying to a treatment program should therefore be accepted for a trial of treatment while further research on greater numbers of subjects may eventually identify predictors of successful outcome.