The authors' objective was to determine circadian blood pressure behavior and the prevalence of orthostatic hypotension in patients with cardioinhibitory carotid sinus syndrome. A prospective consecutive series of 160 patients (mean age, 72 [65-83]) with recurrent syncope attributed to cardioinhibitory carotid sinus syndrome was recruited. Mean maximal slowing of heart rate was 4.5 seconds (3.0-5.5 seconds) during carotid sinus massage. Patients had cardiovascular assessments, including 24-hour ambulatory blood pressure measurements (recordings every half-hour during daytime, hourly at night) and morning orthostatic blood pressures before pacemaker implants. Ambulatory measurements were compared with those of 98 age- and sex-matched controls. Nocturnal systolic blood pressure (130.0±21.0 vs. 122.1±16.7 mm Hg; p<0.005), diastolic blood pressure (72.8±12.5 vs. 68.7±9.7 mm Hg; p<0.005), and heart rate (66.5±9.4 vs. 65.2±9.7 bpm; p<0.005), were significantly higher in patients and independent of cardiovascular medication, cardiovascular diagnoses, and orthostatic hypotension. Almost one half of carotid sinus syndrome patients also had orthostatic hypotension. Blood pressure behavior is abnormal in patients with carotid sinus syndrome as represented by altered nocturnal blood pressures and high prevalence of orthostatic hypotension.