OBJECTIVES: Resistant hypertension is defined as blood pressure (BP) that remains above goal in spite of the concurrent use of three antihypertensive agents from different classes.  Some patients with resistant hypertension do not receive further treatment, potentially increasing the overall burden of disease on the healthcare system through increased healthcare use. To examine the burden of resistant hypertension to the UK healthcare system and explore the potential cost resulting from non-treatment of resistant hypertension. METHODS: The Health Improvement Network computerized data from 6.8 million patients in 382 practices was used to randomly select 9,000 patients with probable or confirmed resistant hypertension.  Patients were characterized by number of therapies received according to NICE treatment guidelines (three therapies: step 3 vs. four or more, step 4).  Blood pressure was used to classify patients as controlled or uncontrolled hypertension.  Associations between covariates and patient status were examined using analysis of variance and logistic regressions.  Pattern of care was assessed for patients in each category using descriptive statistics.  RESULTS: Mean age of patients with hypertension included in the study was 68.8 (SD=11.5).  Among patients in step 3 at baseline, 57.2% had uncontrolled BP (mean BP 151/81 v. 127/73); among patients in step 4, 57.9% were uncontrolled (mean BP 153/80 v. 136/72).  After two years of follow-up, approximately 25% of patients did not receive treatment recommended by NICE guidelines.  Older male patients with diabetes or kidney disease were more likely to have resistant hypertension or uncontrolled BP at either step 3 or 4.  CONCLUSIONS: A large proportion of patients with hypertension do not achieve BP control despite maintaining three or more antihypertensive therapies.  The impact of not treating these patients with appropriate therapies can substantially contribute to overall burden of hypertension borne by the UK healthcare system.