A common thread among health behavior theories is the importance of perceived control, often defined within the health psychology literature as locus of control. Inconsistencies have been found regarding the role of locus of control in predicting health behaviors. These inconsistencies may be resolved by exploring interactions between internal locus of control and other perceived control constructs such as self-efficacy and outcome expectancy. The present study tested the interaction of internal locus of control, self-efficacy and outcome expectancy in relation to HbA1c in patients with Type 2 diabetes. One hundred and nine medical patients who were diagnosed with Type 2 diabetes, predominantly from an African American as well as disadvantaged background, participated in the study. HbA1c was used to indicate gradations of medical regimen adherence. A three way interaction among the perceived control measures was related to HbA1c. Patients who reported low self-efficacy and low outcome expectancy tended to benefit the most from high internal locus of control. However, for patients with low self-efficacy and high outcome expectancy, higher scores on internal locus of control were related to poorer HbA1c levels. Future research examining perceived control constructs may benefit from investigating the interacting effects of such variables when evaluating health behaviors.