Objective: To examine the relationship between adherence to antidepressant medications and HbA(1c) levels among patients with diabetes in a managed care setting. Method: The analysis included measures of HbA(1c) levels before, during, and after initial antidepressant use among 568 patients with diabetes enrolled in the Harvard Pilgrim Health Care insurance plan from 1991-1995. Adherence was defined as four refills in a six-month period after the first antidepressant prescription. General linear models using SAS PROC MIXED were used to estimate the effects of covariates including antidepressant adherence on HbA(1c) levels over time, comparing patients who were adherent to antidepressant medications to those patients who were non-adherent to antidepressant medications. Results: Adherence to antidepressant treatment was not significantly associated with HbA(1c) levels among diabetic patients who are antidepressant users. Younger age, use of insulin and oral medications, and female gender were all significantly associated with HbA(1c) levels over time. Conclusions: Although we did not observe any association between level of adherence to antidepressant therapy among diabetic patients and levels of glucose control, our results confirm previously established associations between patient characteristics and glycemic control. Further research is needed to disentangle the complex relationship among antidepressant treatment adherence and diabetes outcomes.