The aim of this study is to characterize patients with chronic pain in methadone maintenance treatment (MMT). Between September and December, 2003, 170 consecutive patients from an MMT clinic participated in a questionnaire survey on pain (duration and severity). Chronic pain was defined as current pain lasting for >or=6 months. The patients' maintenance methadone dosage and urine tests for drug abuse during the month before and of the survey were recorded. Of the 170 patients, 94 (55.3%) experienced chronic pain. They had a significantly higher proportion of chronic illness (74.5%) compared to non-pain patients (44.7%) (Fisher's Exact Test P<0.0005). Twelve (12.8%) of the chronic pain patients scored their pain as mild, 38 (40.4%) as moderate, 22 (23.4%) as severe and 22 (23.4%) as very severe. Pain duration significantly correlated with pain severity (Pearson R=0.3, P>0.0005) and was significantly associated with methadone daily dosage: patients with pain duration of >or=10 years (n=26) were receiving the highest methadone dosage (182.1+/-59.2 mg/day), those with pain duration from 1 to 10 years (n=59) 160.9+/-56.2 mg/day, and those with pain duration of <1 year (n=9) 134.2+/-73.2 mg/day. Patients in the non-pain group (n=76) were receiving 147.1+/-52.8 mg/day of methadone (ANOVA, F=3.1, P=0.03). We conclude that pain duration and severity significantly correlated. Although methadone was not prescribed for the treatment of pain but rather for opiate addiction, the patients in the MMT clinic with prolonged pain were prescribed a significantly higher methadone dosage compared to patients with short pain duration, and non-pain patients.