Context: Modifiable risk factors in older methadone maintenance treatment (MMT) patients may put them at a greater risk of acquiring chronic diseases. The paucity of literature regarding the well-being and service needs of older MMT patients required investigation to determine whether these patients are treated for and adhere to chronic disease medications(s) comparably to those not on MMT. Objective: This study compared the proportion of MMT patients to a matched control group treated with first-line medications for four chronic diseases: hypertension, chronic obstructive pulmonary disease (COPD), diabetes mellitus and depression. As a secondary outcome measure, this study also examined the adherence comparability between the two groups. Method: This case control study used prescription claims data from the BC Ministry of Health’s PharmaNet database from October 1, 2008 to December 31, 2009. Each MMT patient was individually matched with a control subject in terms of age, sex, social assistance coverage and local health area. Both groups consisted of 143 men and 56 women for a total of 400 participants. Persons 50 years of age and older, residents of BC, and had prescriptions filled during October 1, 2008 to December 31, 2009, were randomly selected from the PharmaNet database. Results: Odds ratios (ORs) were calculated to compare the odds of MMT patients to non-MMT patients on a first-line medication for each chronic disease under investigation. ORs were 0.865 for hypertension (ns), 0.738 for diabetes (ns) and 4.176 for depression (p <0.001). For COPD the OR could not be calculated as no controls were treated for COPD; however, 11.6% of the MMT group were prescribed COPD medications which was significantly higher than the controls (p<.001). Adherence was calculated using continuous measures of medication availability (CMA) “by patient” and “by medication class” during patients’ persistent periods (continuous use periods) CMA(1), as well as the entire study period CMA(2). By patient, the mean CMA(1) showed no difference between the groups (non-MMT group: 91.9%, SD=15.8, CI=95% vs MMT group: 89.7%, SD=22.2, CI=95%). The mean CMA(2) was statistically different (p<0.05) between the groups (non-MMT group: 70.5%, SD=25.3, CI=95% vs MMT group: 60.8%, SD=29.1, CI=95%). By medication class, CMA(1) was 80-100% for most medication classes for both groups except for insulins and inhalers in the MMT group which fell between 40-79%. The CMA(2) for most medication classes was 60-86% in the non-MMT group and 30-76% in the MMT group. However, the differences between the groups were not statistically significant. Conclusion: Odds ratios for the treatment of all four chronic diseases differed. Therefore, looking at each chronic disease separately may be worthwhile to suggest potential targets for intervention. Disease-specific tailored interventions related to lifestyle risk factors, comorbid medical conditions, and adherence to chronic medications could potentially improve the overall health of older MMT patients. However, development of appropriate interventions and treatments requires research that properly recognizes the physical and mental health problems faced by older MMT patients (Rosen, Hunsaker, Albert, Cornelius, & Reynolds III, 2010). / Graduate