In 370 opioid-dependent patients included consecutively in a low-threshold methadone maintenance program, the effect of different variables on the retention rate was assessed. The variables included the patients' age, sex, family situation, employment status, length of heroin use, current route of drug consumption, previous treatments, current consumption of cocaine, alcohol and benzodiazepines, needle sharing, HIV serostatus and methadone dose. The retention rate after 2 years of methadone maintenance was 72%. Dose of methadone > 80 mg/day, age > 30 years, living with family or stable partner and non-current use of alcohol were significant predictive variables for retention.