Purpose: Acute urinary Retention in children is a relatively rare entity. There are a variety of causes that are poorly defined in the literature. We review our cases of acute urinary Retention in children at three major pediatrics centers in Iran. Materials and Methods: Between 1996 and 2003, children (up to 14 years old) who had been referred due to acute urinary Retention were examined. Urinary Retention was defined as inability to empty the bladder volitionally for more than 12 hours with a urine volume greater than expected for age or a palpably distended bladder. All data from the patients past medical history, physical examination, and laboratory and radiographic assessments were collected. Also, cystourethroscopy and urodynamic procedures had been carried out according to patients conditions. Patients with secondary urinary Retention, including those with surgical history, immobility or chronic neurological disorders, mental retardation, and drugs or narcotics consumption were excluded from study. Results: There were 86 patients meeting the inclusion criteria, consisting of 58 males with a median age of 4 years (range 1 month to 14 years) and 58 females with a median age of 4 years (range 4 month to 14 years). Etiologies were lower urinary tract stone in 27.9%, neurological disorders in 10.4%, trauma in 10.4%, local inflammatory causes in 9.1%, urinary tract infection in 7.4%, ureterocele in 7.4%, benign obstructing lesions in 5.8%, iatrogenic in 5.8%, constipation in 4.6%, imperforated hymen in 3.5%, and large prostate utricle, urethral foreign body, and rhabdomyosarcoma each in 1 case (1.1%). Conclusion: The most common cause of acute urinary Retention was lower urinary tract stone in our pediatric cases. Ureterocele and stone were the main findings in girls and boys, respectively, and urinary Retention in boys was twice as prevalent as that in girls.