This paper describes an unusual, familial bilateral papillary cystadenoma of the epididymis found in three siblings. The histological characteristics of the tumor were: 1) papillary proliferation of clear cells, consisting of both tall columnar and round ovoid cells, in the efferent duct epithelium; and 2) cystic dilatation of the duct with colloidal material. The present cases were unique in two respects: 1) familial bilateral papillary cystadenomas probably associated with Lindau's disease have not been reported previously: and 2) electron microscopic observations suggested that the tumors originated from the efferent duct.