Introduction Focal segmental glomerulosclerosis(FSGS) can occur secondary, and Cushing’s syndrome and sarcoidosis are rare diseases for which a causal relationship has been confirmed. Cushing's syndrome is characterized by excessive elevation of cortisol concentration. In rare cases, treatment of Cushing's syndrome can lead to exacerbation of diseases that respond to glucocorticoid. Here, we report a rare case of post-treatment sarcoidosis in a patient diagnosed with FSGS and Cushing's syndrome, who simultaneously had three related disorders. Case A 30-year-old woman presenting generalized edema visited emergency room. The initial blood pressure was 170/90 mm/hg. Urinary analysis showed microscopic hematuria and nephrotic range proteinuria. The serum aldosterone/renin ratio was not elevated, and the low dose dexamethasone suppression test suggested ACTH-independent Cushing’s syndrome. Computed tomography showed right adrenal adenoma. The renal biopsy result was FSGS. Laparoscopic right adrenalectomy was performed. The patient was treated with hydrocortisone replacement and the patient's edema and proteinuria improved. After 6 months, the patient visited our clinic due to dyspnea and nodules in the left wrist, elbow and knee. A chest radiograph revealed bilateral hilar lymphadenopathy. Biopsy was performed on the skin nodules and lung lymph nodes, and as a result, non-caseating granuloma was found and sarcoidosis was diagnosed. The patient was started on methylprednisolone therapy. Conclusion We report a patient with a combination of FSGS, Cushing's syndrome and sarcoidosis. High cortisol levels can lead to immunosuppression, and as a result, hidden diseases such as sarcoidosis can occur if the immune status recovers after treatment for Cushing's syndrome. Appropriate follow-up is important after excessive cortisol secretion is resolved, and we highlight the potential for developing autoimmune or inflammatory diseases after treatment. When evaluating with the possibility of hidden disease, the possibility that three or more diseases may be related to each other should also be taken into consideration.