125 boys with idiopathic GH deficiency who received GH treatment were followed until they reached their final height. In 85 patients who had spontaneous puberty (group I), the mean final height was 151.5 ± 6.6 cm. In 23 patients with combined GH and gonadotropin deficiency (group II) whose pubertal development was induced artificially at age 19.4 ± 2.1 years, the mean final height was 163.7 ± 3.9 cm (p < 0.01 vs. group I). Final height was strongly related to height at the onset of pubertal development in combined groups I and II when the time of gonadal replacement treatment was taken as the onset of pubertal development in group II. In 17 patients (group III) who developed spontaneous puberty, gonadal suppression treatment was started at their early stage of puberty and was continued for a mean duration of 4.3 ± 1.1 years. The mean final height in group III was 157.9 ± 3.0 cm (p < 0.01 vs. group I, group II). Longitudinal growth pattern analysis demonstrated that this beneficial effect on final height by gonadal suppression treatment was attributed to the elongation of pubertal growth spurt and pubertal height gain.