Substitution therapy of glucocorticoid is a major part of the treatment for 21-OHD (21-hydroxylase deficiency). However, the therapy causes two major adverse effects, impairment of linear growth and obesity, so that collecting precise growth data is essential for optimizing the therapy. We longitudinally evaluated the linear growth and the body composition of Japanese 21-OHD patients during childhood. For the present study, we chose 16 patients (eight of each sex) who were diagnosed during the newborn period, and continuously observed them in our institute until they were at least 15 years old. All patients were treated according to the guidelines from The Japanese Society for Pediatric Endocrinology. The final height standard deviation score (Ht-SDS) of all the patients was -1.18 ± 0.85 SD, and no significant differences were observed between males and females or between the simple virilizing form and the salt wasting form. As previously reported, in spite of nearly normal height at the onset of puberty, the pubertal height gains were severely impaired, resulting in reduced final heights. Body composition of the patients was evaluated with BMI-SDS. Our longitudinal data showed that BMI was increased up to +1.23 SD in males and up to +1.75 SD in females, and that adiposity rebound was precipitated. Our study should alert physicians to the risk of metabolic syndrome and provide a framework for further studies of metabolic syndrome in 21-OHD patients.