The study aimed to determine characteristics of addicts on methadone maintenance therapy (MMT), which are related to the level of social functioning, with emphasis on the role of social support. In a prospective study, opiate addicts (n=150) who were on MMT completed the Pompidou questionnaire, the Social Adaptation Self-evaluation Scale (SASS) and the Multidimensional Scale of Perceived Social Support (MSPSS). Statistical data processing was based on testing the difference between features that best distinguish subgroups of addicts who were dissatisfied, moderately satisfied and satisfied with their social functioning. Opiate addicts up to 30 years of age had a statistically higher score on SASS scale than addicts over 30; addicts who are dissatisfied are mainly unemployed and have average or above-average family/community financial status; opiate addicts who were moderately satisfied with their social functioning were three years or longer on MMT; paradoxically, the highest mean value of score on MSPSS scale dominated among addicts who are dissatisfied with their social functioning. These results indicate that age, employment, financial status, duration of MMT are the characteristics of addicts which are related to the level of social functioning. Social support is most perceived by addicts who are dissatisfied with their social functioning.