Cushing's disease is a condition in which hypercortisolism develops due to excessive hypophyseal adrenocorticotropic hormone production. It is rare in childhood. In this paper, we report the case of a 10-year-old male patient with hypophyseal microadenoma-related Cushing's disease who presented with obesity and was found to show poor height growth at follow-up. The diagnosis was confirmed with inferior petrosal sinus sampling, and the adenoma was successfully removed by transsphenoidal surgery. While adrenal axis suppression continued for approximately 1 year, clinical improvement was clearly observed after the third month following surgery. The findings in this patient demonstrate that decreased growth rate despite rapid weight gain in children can be early sign of Cushing's disease and emphasize the importance of monitoring of growth in obese children.