OBJECTIVES: This study sets out to explore the adherence to British Hypertension Guidelines in choosing first-line treatment for blood pressure by general practitioners (GPs) in the UK. These currently recommend thiazide diuretics as the preferred choice and beta-blockers as an alternative initial treatment for most patients. METHODS: The data on choice of blood pressure treatment recorded at first diagnosis of hypertension were obtained from a UK GP computer database, IMS Disease Analyzer - Mediplus. The records covered the one-year period March 2002 to February 2003. The database holds the records of 564 GPs and 948,958 registered patients. RESULTS: Of 8,540 patients with at least three months history on the database and a new diagnosis of hypertension within the year of analysis, initial treatment was as follows: 36.5% thiazide diuretic; 22.4% beta-blocker; 17.8% ACE inhibitor; 10.1% calcium channel blocker; 4.0% angiotensin-2-receptor antagonist; 2.1% alpha-blocker. 16.4% were not started immediately on antihypertensive therapy. Of those that did, 4.6% received first treatment as a combination of two drugs (hence the total figures do not add up to 100%). CONCLUSIONS: This study suggests that first-line treatment is often using a drug that is not in accord with current National policy as only 58.9% were started on recommended first-line therapy. Choices from other drug classes tend to be more expensive, and there is less evidence of benefit. In particular the 4.6% starting treatment with combination therapy appears at odds with the policy to start with a single agent. Co-morbidity such as diabetes or bladder outflow obstruction may explain the choice of other agents; for example angiotensin-inhibiting drugs in diabetes, but the prevalence of these conditions is not sufficient to explain this variation from the guidelines. This choice of drugs may reflect heavy marketing of these newer products rather than evidence-based medicine.