Antihypertensive medication noncompliance is common and leads to substantial morbidity for patients and increased health care costs for managed-care organizations. A retrospective cohort study using pharmacy prescription profiles to estimate noncompliance was conducted to determine important risk factors for patient noncompliance with antihypertensive therapy for Medicaid enrollees participating in a managed-care plan. The pharmacy and claims data for 1395 patients with uncomplicated hypertension who were enrollees of Tennessee's Medicaid managed-care program were analyzed to determine the frequency of the enrollees' failure to obtain timely antihypertensive medication refills (hereafter referred to as refill failure) and to identify the predictors of refill failure. Overall, refill failure occurred in 33% of 7413 refill opportunities studied, whereas refill failure occurred in 32% of the cases in which medication was dosed once daily and in 35% of the cases in which medication was dosed more than once daily. For patients taking alpha-blockers, there was a significantly lower rate of refill failure (11.0%) than for patients taking angiotensin-converting enzyme inhibitors, direct vasodilators, and thiazide diuretics. Patients taking calcium channel blockers, had a significantly lower rate of refill failure (38.5%) than for patients taking thiazide diuretics (45.5%). Younger age, medication class, multiple-daily dosing regimen, and fewer provider visits were all found to be significant independent predictors of refill failure, whereas gender and regimen complexity were not significant predictors in this population. Health care systems planning pharmacy-based interventions to improve patient compliance with antihypertensive medication for patients in a Medicaid managed-care program can expect to encounter high levels of refill failure and may want to target enrollee subgroups by age, medication class, or dosing regimen for intensive intervention efforts.