Objective: The purpose of this study was to determine the postoperative postvoid residual volume that predicts a voiding efficiency after operation for incontinence and prolapse. Study Design: Ninety-nine patients met the criteria for inclusion. The patients' bladders were filled retrograde through gravity, through a Foley catheter, with 300 mL of sterile water, or by subjective fullness. The catheter was then removed, and the patient was asked to void spontaneously into a measured urine collection device (“Texas hat”). A postvoid residual was then calculated (amount voided minus amount inserted). The Foley catheter was reinserted for patients with a postvoid residual of >50%. These patients were instructed to follow-up in the office in 1 week, at which time the test was repeated. This process continued until the patient had a postvoid residual of ≤50% or was taught intermittent self-catheterization. Results: Ninety patients were available for follow-up. The overall failure rate (defined as cases that required reinsertion of a catheter) was 7.8%. No patient with a postvoid residual of ≤32% required reinsertion of a catheter. Conclusion: With the use of this simple bedside test, voiding efficiency was predicted in 92% of patients who voided ≥50% of the amount inserted and in 100% of patients who voided ≥68%. (Am J Obstet Gynecol 2002;187:49-52.)