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 greater than or equal to 150 cm3, thus decreasing the incidence of some major postoperative complications that can occur due to unnecessary catheterization.