Medication nonadherence represents a modifiable risk factor for patients with hypertension. Identification of nonadherent patients could have significant clinical and economic implications in the management of uncontrolled hypertension.We analysed the results of 174 urinary adherence screens from patients referred to Addenbrooke's Hospital, Cambridge, for uncontrolled hypertension. Cases were identified for evaluation by results of liquid chromatography-tandem mass spectrometry of urine samples (males: 91; females: 83; age range: 17-87). We performed a binary logistic regression analysis for nonadherence using age, sex, and number of medications prescribed (both antihypertensives and non-antihypertensives separately) as independent predictors. Rates of nonadherence for individual antihypertensive drugs were calculated if prescribed to ≥10 patients.The overall rate of nonadherence to one or more prescribed antihypertensive medications was 40.3%. 14.4% of all patients were nonadherent to all prescribed antihypertensive medications (complete nonadherence), whereas 25.9% of all patients were nonadherent to at least 1, (but not all) prescribed antihypertensive medications (partial nonadherence). 72% of patients were prescribed ≥3 antihypertensives And for every increase in the number of antihypertensive medications prescribed, nonadherence increased with adjusted odds ratios of 2.9 (P < .001). Logistic regression showed that women were 3.3 times more likely to be nonadherent (P = .004). Polypharmacy (≥6 medications prescribed for hypertension and/or concomitant comorbidities) was prevalent in 52%. Bendroflumethiazide and chlortalidone demonstrated the highest and lowest nonadherences respectively (45.5% and 11.8%).Rate of nonadherence in patients with hypertension was significantly impacted by sex and number of antihypertensive medications prescribed. Understanding these factors is crucial in identifying and managing nonadherence.