Introduction: Despite the wide spread use of modern portable ultrasound equipment to measure the postvoid residual urine, its accuracy and reliability has been questioned. We investigated the accuracy of postvoid residual urine measurement by portable abdominal ultrasound equipment in end-stage renal disease patients who are under either hemodialysis or peritoneal dialysis. Materials and Methods: A total of 21 male (range: 25-44 years, mean age: 32 years) end-stage renal disease patients were studied. Ten were under peritoneal dialysis and 11 under hemodialysis. After uroflow-metric study, all patients were evaluated with portable abdominal ultrasound equipment (BladderScan BVI 3000, Diagnostic Ultrasound Corporation, WA) by both a technician and a physician and they were subsequently catheterized with a 10F catheter to measure the residual urine volume in the urinary bladder. Postvoid residual urine volume results by portable abdominal ultrasound equipment and urethral catheterization were analyzed. Results: We found portable abdominal ultrasound to be very accurate to measure the volume of postvoid residual urine in hemodialysis patients(r = 0.921, P < 0.05 by physician and r = 0.904, P < 0.05 by technician). However, accuracy was the worst in peritoneal dialysis patients (r = 0.055, P = 0.88 by physician and r = 0.336, P = 0.343 by technician). The technician or physician use of the equipment did not change the accuracy profile of the equipment in both hemodialysis and peritoneal dialysis patients. Conclusions: Portable abdominal ultrasound equipment may be an unreliable method to measure postvoid residual urine volume in peritoneal dialysis patients. Neurourol. Urodynam. 24:358-361, 2005. (c) 2005 Wiley-Liss, Inc.