Circadian blood pressure (BP) rhythm was prospectively studied by ambulatory 24-h monitoring in normotensive (n = 27) and hypertensive (n = 41) patients with stable progression of chronic renal insufficiency, and in matched control groups (healthy subjects: n = 28 and patients with essential hypertension: n = 47) without renal disease. The follow-up period lasted 24 months. The renal patients showed a disturbance in the 24-h profile of BP, with significantly blunted nocturnal pressure reduction as compared with the respective control groups (p<0.01 and p<0.001, respectively). In addition to the rearrangement of circadian rhythm, the normotensive and hypertensive renal patients displayed a wider distribution of systolic and diastolic BP values and a greater nocturnal variability. Among the normotensive and hypertensive patients with chronic renal insufficiency, a significant correlation was found between the decline in creatinine clearance over the 24-month period and the average nighttime diastolic BP (r = 0.526; p<0.01 and r—0.613; p = 0.001, respectively) and nocturnal diastolic fall (r = 0.612; p<0.001 and r = 0.496; p<0.07, respectively). These data offer support for the view that renal normotensive patients are exposed to a relative hypertension at nighttime and that renal hypertensive subjects can be underestimated in their hypertensive status if the measurement of BP is confined to daytime. In both groups, nocturnal BP overload can accelerate the progression rate of renal insufficiency.