To determine what volume a child can normally store in the bladder at a safe pressure 923 pediatric urodynamic studies were reviewed, and 69 examinations done on 17 boys and 52 girls were considered normal. Patient ages were recorded and body surface areas were calculated. A continuous intermediate flow water cystometrogram had been performed. Total bladder capacity in milliliters, full resting pressures (cm. water), and the volumes (milliliters) and percentages of the total bladder capacity stored at detrusor pressures of less than 10, 20, 30 and 35 cm. water were measured. We found that 98.1% of the total bladder capacity could be stored at a detrusor pressure of less than 20 cm. water in more than 95% of the children independently of age or body surface area and 99.9% could be stored at a detrusor pressure of less than 30 cm. water. An approximation of the minimal acceptable total bladder capacity for age can be calculated by 16(age) + 70 in ml. According to our results, we proposed criteria for good storage characteristics of the bladder in children.