The mechanisms underlying the relationship between health literacy, numeracy, and glycemic control are unclear. We explored the role of diabetes self-efficacy in the predicted pathway linking health literacy and numeracy to glycemic control (A1C). Adults with type 1 or type 2 diabetes mellitus (N = 383) were enrolled in a cross-sectional study at primary care and diabetes clinics at three medical centers. Data collected included demographic information, health literacy, general numeracy, and A1C. Path models estimated relations among health literacy, numeracy, and diabetes self-efficacy as predictors of A1C. Health literacy (r = 0.14, p < .01) and numeracy (r = 0.17, p < .001) were each associated with greater diabetes self-efficacy, and greater diabetes self-efficacy was associated with lower A1C levels (r = -0.25, p < .001). When considered in combination, numeracy was related to diabetes self-efficacy (r = 0.13, p < .05), and the effect of health literacy on diabetes self-efficacy was reduced to non-significance (r = 0.06, p = .30). Health literacy and numeracy are each associated with greater diabetes self-efficacy, and greater diabetes self-efficacy is associated with lower A1C levels. Diabetes self-efficacy may be an important target of interventions to improve diabetes control and promote health equity related to health literacy and general numeracy skills needed for diabetes management.