OBJECTIVE To compare the 24-hour blood pressure (BP) pattern in physiologic pregnancy, pregnancy-induced hypertension, preeclampsia, and chronic hypertension. METHODS We investigated four groups of women with singleton pregnancy: 73 controls, 48 patients with pregnancy-induced hypertension, 38 with preeclampsia, and 53 with mild to moderate chronic hypertension. The 24-hour BP monitoring was performed longitudinally in controls and in patients with chronic hypertension, and at the time of diagnosis in those with pregnancy-induced hypertension or preeclampsia. RESULTS Nineteen thousand eight hundred seventy-two BP measurements were analyzed. In controls, the mean values of BP indices were lower than those first reported in nonpregnant women, and the acrophase was always localized in the first part of the afternoon. In pregnancy-induced hypertension and especially in preeclampsia, besides the obvious quantitative increase in BP, circadian BP oscillations were less pronounced than in controls, and the severity of hypertension seemed to favor the loss of diurnal rhythm. Conversely, in chronic hypertension, circadian oscillations were the same as in controls. CONCLUSIONS Standardized 24-hour BP monitoring during pregnancy allows quantitative and qualitative evaluations of the hypertensive status. However, if such a technique is used routinely in every clinical setting, we should establish specific thresholds of normality for pregnancy.