We report a case of infectious perinephric urinoma in a 73-year-old woman who had a neurogenic bladder with vesico-ureteral reflux. The patient was admitted to our emergency room with right lumbago and high fever. Ultrasounds and computed tomography demonstrated a right large perinephric cystic mass, bilateral hydronephrosis and much residual urine. Percutaneous drainage of the cystic mass was performed with an indwelling urethral catheter. The content of the mass was urine infected with Escherichia coli. Antibiotic therapy was performed successfully and we then examined the cause of the urinoma. A urodynamic study demonstrated a low-compliance small bladder and detrusor-sphincter dyssynergia. A voiding cystourethrogram revealed right grade III vesicoureteral reflux. The patient was unable to be cleared with intermittent catheterization and had an indwelling urethral catheter inserted. In 1 year, the voiding cystourethrogram showed no vesicoureteral reflux and the patient was well with no evidence of recurrent urinoma without the urethral catheter. There have been only two reported cases of urinoma caused by neurogenic bladder with vesico-ureteral reflux in children and this is the first case reported in an adult.