Background: In the past few years there has been a growing amount of information about renal dysfunction and cardiovascular risk. The objectives of this study were to assess the prevalence of renal dysfunction and evaluate the relation between renal function and cardiovascular risk in patients with essential hypertension., Methods: A multicenter, cross-sectional survey of unselected patients with essential hypertension attending primary care settings in Spain was performed between june and november 2004. Renal function was evaluated with the abbreviated equation of the Modification of Diet in Renal Disease study. Renal insufficiency was defined as an estimated glomerular filtration rate <60 ml/min/1.73 m2., Results: Eighty-eight investigators from 50 centers recruited 2130 patients being mean age 65.6 +/- 11 years and female 53%. Prevalence of diabetes, lipid abnormalities, and previous cardiovascular disease were 30.3%, 45.9%, and 42.1% respectively. Prevalence of renal insufficiency was 32.4% (95% CI 30.4-34.4). Patients suffering from renal insufficiency showed a higher prevalence of cardiovascular disease when comparing with those with an estimated glomerular filtration rate = or >60 ml/min/1.73 m2 (56.2% vs. 35.3%, OR 2.35, 95% CI 1.95-2.82, p < 0.001). A logistic regression analysis showed that the relation of renal dysfunction with cardiovascular disease was independent of other variables or classical cardiovascular risk factors as age, female sex, diabetes, smoking, hypercholesterolemia, and systolic blood pressure., Conclusions: Renal insufficiency was present in 32.4% of patients with essential hypertension attending primary care settings. Cases with renal dysfunction showed a higher cardiovascular risk. Hypertensive patients with renal insufficiency should be considered as candidates for an aggressive approach of cardiovascular risk management.