Transverse and sagittal bladder diameters were measured with real-time ultrasound in 80 patients (100 measurements) during the first 2 days of postvaginal hysterectomy to assess the residual bladder volume and compared with the catheterization volume for the same patients. The sonographic method, with a 97.7% specificity and a negative predictive value of 89.5%, proved to be specific enough to eliminate the necessity of routine catheterization for measuring residual bladder volumes of > 150 cm3, thus decreasing the incidence of some major postoperative complications that can occur due to unnecessary catheterization.