Approximately 30 cases of carcinoid tumor of the kidney have been reported in the English literature, including three cases found as components of teratomas. Renal composite tumors associated with somatostatinoma have not been described. A 53-year-old female presented with an incidentally found right renal cystic lesion. Computed tomography demonstrated a cystic lesion associated with a solid nodule in the right kidney and postcontrast dynamic MRI revealed enhancement of the solid nodule. The patient underwent radical nephrectomy for the kidney lesion and is now well without recurrence 21 months after the operation. From the histopathological findings we diagnosed the cystic lesion as a composite tumor composed of mucinous cystadenoma and carcinoid tumor. Immunohistochemistry demonstrated the majority of cells of in carcinoid portion to be positive for antisomatostatin staining. The present case is the first documented composite tumor of mucinous cystadenoma and somatostatinoma of the kidney.