Objective To investigate whether ambulatory blood pressure monitoring in patients with inverted U waves before gynecologic operation is helpful to identify undiagnosed hypertension. Methods Fifty-four patients with U wave inversion received ambulatory blood pressure monitoring before gynecologic operation. The correlations among U wave inversion, 24-hour average blood pressure, diurnal blood pressure, nocturnal blood pressure, nocturnal systolic pressure, nocturnal diastolic pressure, and circadian rhythm were analyzed. Results For 24-hour average blood pressure, normal and elevated patients were 16 (29.6%) and 38 (70.4%)(P<0.01). For nocturnal blood pressure, normal and elevated patients were 12 (22.2%) and 42 (77.8%)(P<0.01). For systolic pressure, diastolic pressure, and circadian rhythm, normal and abnormal ratios were also significantly different (P<0.01). Conclusion Ambulatory blood pressure monitoring in patients with U wave inversion is helpful to identify patients with undiagnosed hypertension or uncontrolled hypertension and to achieve better blood pressure control.