In England, the National Institute for Health and Care Excellence (NICE) produces guidelines for the management of hypertension. In 2006, the NICE guidelines introduced an ethnic-age group algorithm based on the 2004 British Hypertension Society guidelines to guide antihypertensive drug prescription.A longitudinal retrospective study with 15933 hypertensive patients aged 18 years or over and registered with 28 general practices in Wandsworth, London in 2007 was conducted to assess variations in antihypertensive prescribing. Logistic models were used to measure variations in the odds of being prescribed the 2006 NICE first line recommended monotherapy among NICE patient groups over the period.From 2000 to 2007, the percentage of patients prescribed the recommended monotherapy increased from 54.2% to 61.4% (p < 0.0001 for annual trend). Over the study period, black patients were more likely to be prescribed the recommended monotherapy than younger non-black patients (OR 0.16, 95% CI 0.12-0.21) and older non-black patients (OR 0.49, 95% CI 0.37-0.65). After the introduction of the NICE guidelines there was an increase in the NICE recommended monotherapy (OR 1.44, 95% CI 1.19-1.75) compared with the underlying trend. Compared to black patients, an increase in the use of recommended monotherapy was observed in younger non-black patients (OR 1.49, 95% CI 1.17-1.91) but not in older non-black patients (OR 0.58, 95% CI 0.46-0.74).The introduction of the 2006 NICE guideline had the greatest impact on prescribing for younger non-black patients. Lower associated increases among black patients may be due to their higher levels of recommended prescribing at baseline. The analysis suggests that guidelines did not impact equally on all patient groups.