OBJECTIVE:: An attenuation of the physiological day-night blood pressure (BP) reduction is an important predictor of cardiovascular (CV) events and death. We compared circadian BP profile in treatment-naive HIV-infected patients and in healthy control subjects. METHODS:: Fifty-two antiretroviral therapy-naive HIV-infected patients (85\% men, age 39 ± 11 years, BP 125/78 ± 11/9 mm Hg) and 156 age- and BP-matched HIV-negative controls (85\% men, age 39 ± 10 years, BP 125/78 ± 9/7 mm Hg) underwent 24-hour BP monitoring. Subjects with a nocturnal reduction of systolic BP <10\% were defined as "nondippers." RESULTS:: Nighttime BP was higher in HIV-infected subjects (113/69 ± 11/9 vs 109/67 ± 8/6 mm Hg, P = 0.008/0.005). Nocturnal systolic/diastolic BP reduction was 8.8/13.2\% in HIV-positive patients and 11.7/17.2\% in HIV negative (P = 0.002/0.001). The prevalence of "nondippers" was 35\% and 15\%, respectively (P = 0.003). In multivariate analysis, nocturnal systolic BP fall was negatively associated to HIV infection (β = -0.22, P = 0.001). HIV viral load, low CD4 cell count, and AIDS progression risk were all related with a flattened day-night BP profile (P < 0.01). CONCLUSIONS:: HIV infection per se negatively affects circadian BP rhythm. These findings, obtained in subjects without major CV risk factors and antiretroviral naive, suggest that day-night BP changes may play a role in the HIV-related increase in CV risk.