In order to establish the normal range of urinary growth hormone (GH) level for age and sex, which is important in the clinical application of urinary GH to diagnosis, we measured GH in the first morning urine specimens of 270 normal subjects aged 3 to 20 years. Urinary GH levels in patients with documented GH deficiency were compared with those of the normal controls. In normal subjects, urinary GH levels showed a statistically significant change with age. They were relatively high in infancy and mid-puberty, reaching a peak at 11 to 12 years in girls and at 13 to 14 years in boys. Urinary GH levels in patients with complete GH deficiency were apparently lower (less than -2.0 SD) than those of the normal children, while the levels in patients with partial GH deficiency overlapped with the normal range. When assessing GH secretion by using urinary GH measurement, consideration of age and sex is required, since the level changes significantly with these factors.