In assessing the quality of medical care, techniques are needed which can predict which patients are likely to have good or poor health outcomes. This study describes one way of identifying a subgroup of hypertensive patients whose diastolic blood pressures (DBP) are at high risk of remaining uncontrolled while under treatment. Medical care and patient variables were measured for 123 hypertensive medical clinic patients. Stepwise discriminant analysis identified a set of six variables which best distinguished between patients with well-controlled and uncontrolled DBP. When measurements of these variables were divided into high and low risk responses for uncontrolled DBP, the number of high risk variables was directly related to the proportion of patients with uncontrolled DBP. The variables also predicted DBP control among 63 patients in an entirely different medical care setting.