OBJECTIVE Referral to ambulatory blood pressure monitoring may have bearing upon blood pressure control and prognosis. We describe sex-related differences in referral for ambulatory monitoring and their prognostic impact. METHODS Between 1991 and 2005, 3957 patients were monitored in our ambulatory monitoring service, of whom 2114 (53%) were women. Demographic and clinical data were analyzed according to sex. RESULTS Age (58+/-15 vs 52+/-17 years, respectively) and body mass index (27.5+/-4.9 vs 26.9+/-4.0 kg/m(2), respectively) were higher in women than men. Treatment for hypertension was more prevalent in women (62% vs 53%, respectively). Clinic systolic blood pressure (148+/-24 vs 146+/-20 mm Hg, respectively) and clinic pulse pressure (65+/-22 vs 59+/-18 mm Hg, respectively) were higher in women compared with men. In women, the white-coat effect was increased, compared with men; 5.2+/-12.4% vs 1.5+/-10.7% systolic, and 5.4+/-11.2% vs 3.6+/-10.3% diastolic. Consequently, women had lower ambulatory blood pressure than men. In women, 24-hour blood pressure was 136+/-17/76+/-10 vs 140+/-15/81+/-10 mm Hg in men, awake blood pressure 141+/-17/80+/-11 vs 144+/-15/84+/-10 mm Hg, and sleep blood pressure was 125+/-19/67+/-10 vs 127+/-18/71+/-11 mm Hg. Age-adjusted ambulatory blood pressure also was lower in women. Ambulatory heart rate was higher in women (P <.0001). Kaplan-Meier survival did not differ by sex (P=.66), despite older age and higher clinic blood pressure. CONCLUSIONS The results might imply that referral was driven by the physicians' overall patient risk perception. The greater magnitude of white-coat effect in women, and correspondingly lower ambulatory blood pressure, might in part account for similar mortality in the face of older age and higher clinic blood pressure.