We performed radiofrequency ablation (RFA) in a 35-year-old woman who suffered from Cushing syndrome caused by functioning adenoma of the right adrenal gland. She had a history of tumor enucleation of functioning adenoma of the left adrenal gland 15 years earlier. However, this time she declined repeated surgical intervention. We performed RFA of the right adrenal adenoma, and the lesion was thought to be well ablated. Cortisol levels decreased to below the lower limit of normal after ablation, but recovered to within the normal range after 1 month using steroid substitution therapy. Although hydrocortisone administration was discontinued 18 months after RFA, cortisol levels remained within the normal range for another 2 years in follow-up.