A cross-sectional survey of 507 in- and out-patients, with diagnosed Type 2 diabetes mellitus (T2DM) was undertaken to study the relationships between personal, disease and treatment-related factors and diabetes control in a tertiary care hospital. On multivariate logistic regression analysis, self-efficacy (odds ratio (OR) =2.94; 95% confidence interval (CI) =1.92-4.54); P<0.001) was the single most important determinant of current diabetes control (HbA1c ≤7%), along with absence of hyperglycemic symptoms in the past year (OR=1.83; 95% CI=1.15-2.93, P<0.01), current treatment with oral medication (OR=1.77; 95% CI=1.17-2.66; P<0.007), and adherence to dietary restrictions (OR=2.7; 95% CI=1.28-5.88; P<0.009). Self-efficacy was itself influenced by educational status, employment, availability of family support, and positive mental attitudes. Our findings suggest that health care delivery inputs, patients' personal characteristics including education and attitude, and family support for care are complexly processed to determine patients' ability to manage their disease, which ultimately influences disease outcomes.