The objective of this study was to investigate the association between NSAID use and blood pressure (BP) among a sample of treated hypertensive patients. A controlled observational study was designed in UK primary care setting. Patients with diagnosed hypertension and currently being prescribed antihypertensive medication registered with four general practices, comparing patients also prescribed NSAIDs (exposed) to those not prescribed NSAIDs (unexposed). Majority of the patients were elderly. Systolic and diastolic pressure were the outcome measures. Data were collected for 184 NSAID users and 762 nonusers with a mean age of 68 years. There was no difference in either systolic (adjusted difference 1.9 mmHg, 95% CI -0.7 to 4.5, P=0.15) or diastolic (adjusted difference 1.0 mmHg, 95% CI -0.3 to 2.3, P=0.15) blood pressure. There was no evidence of any interactions according to categories of age, sex, or number of antihypertensive drugs prescribed. Among NSAID users, there was no evidence of any differences in blood pressure according to NSAID type or dose. In conclusion we found no evidence for an association between NSAID usage and BP control in known hypertensive patients receiving antihypertensive medication in primary care. The reported association between NSAID use and BP control appears much less substantial than has been previously suggested.