The aim of the study was to evaluate the circadian blood pressure (BP) profiles in patients with two forms of Cushing's syndrome, and to compare them to those in patients with essential hypertension. The study included 100 patients with Cushing's syndrome (80 with pituitary adenomas and 20 with adrenal adenomas) and 40 with essential hypertension. Twenty-four-h ambulatory BP monitoring was performed before and after therapy. All 3 groups had similar office-, 24-h-, awake-, and sleep BP mean values. The awake-sleep differences between the patients with two forms of Cushing's syndrome were similar. The night-time BP decline in the patients with Cushing's disease, as well as in those with adrenal adenomas, was significantly lower than that in the patients with essential hypertension. In the patients with both forms of Cushing's syndrome, there was a highly significant decline in the office and ambulatory BP levels after the treatment, and the awake-sleep systolic BP difference became significantly higher. The night-time diastolic BP decline was significantly higher after treatment in patients with adrenal adenomas and not-significantly higher in patients with Cushing's disease. In the patients with Cushing's disease, the duration of hypertension was greater, and lower percentage of normalized BP after treatment was observed in comparison with the patients with adrenal adenomas. The significant negative correlation between duration of the disease and extent of the night-time BP decline suggests that the 'non-dipping' profile is related not only to hypercortisolism itself but also to the severity of hypertension and duration of the disease.