A non-dipping pattern in ambulatory blood pressure monitoring (ABPM) increases the risk of cardiovascular disease. The association between renal function and the dipping pattern has not been studied in a random middle-aged population. This is a cross-sectional population-based study of 226 males and 234 females aged 40 to 62 years. Renal function was assessed with estimated glomerular filtration rate (eGFR). Non-dipping status was defined as a reduction of <10% between the daytime and the nighttime systolic BP. Non-dippers represented 18.7% of the study population. Their mean eGFR was 79.1 (s.d. 15.7) ml min(-1) per 1.73 m(2) as compared with a mean eGFR of 84.1 (s.d. 16.2) ml min(-1) per 1.73 m(2) in dippers (P=0.005); this difference remained significant after adjustments. Subjects in the lowest and in the middle eGFR tertiles had an independently increased risk of non-dipping in comparison with those in the highest eGFR tertile (odd ratios (OR), 2.34 (95% confidence interval (CI), 1.18 to 4.63) and OR, 2.01 (95% CI, 1.06 to 3.83), respectively). This study showed that even a minor deterioration in renal function is associated with increased risk of non-dipping pattern in ABPM in a random middle-aged population.