OBJECTIVES To examine the determinants of demand for health service utilization in a chronic noncancer pain population. METHODS Data were collected from the Opioid Utilization Study (OPUS), an ongoing 1-year, multicenter, prospective, observational cohort study of patients with chronic non-cancer pain receiving opioids. Negative binomial models were used to evaluate determinants of medical service utilization. Dependent variables were: number of medical visits and utilization of alternative/complementary therapy (i.e. acupuncture and massages). Explanatory variables were: physical (PF) and mental function (MF) scores from the Short Form 12 Health Survey® (SF-12), mean cost of medical visits, net household income, insurance type, sex, race and age. RESULTS Of 811 patients, 61.4% were female and 90.9% were white, 94.3% had experienced chronic pain for > 1 year. The mean number of medical visits was 2.9 (SD = 3.6) per month for females and 2.6 (SD = 3.6) for males. On average, patients visited pain clinics once a month (mean = 0.9, SD = 1.17), and visited primary care physicians once every other month. MF, race, income, and mean cost per visit was statistically significant (p<.05). Patients with lower MF were more likely to have higher rates of medical utilization (P <0.001). A one unit increase in MF score was associated with a 1.1% decrease in the rate of medical visits. However, there was no evidence that PF was associated with the rate of medical visits. The mean cost of medical services was statistically significant (p<0.001). A $10 increase in cost decreased the rate of medical visits by 2%. Lower income patients were more likely to consume higher medical services compared to the high income group (p<0.01). CONCLUSIONS MF measures may be useful in predicting medical care utilization. Health care costs were negatively associated with health utilization as is predicted by demand theory.