A syndrome characterized by bilateral, multifocal renal cystadenocarcinomas and nodular dermatofibrosis was found in 43 German shepherd dogs. Affected kidneys varied in weight from normal to 2950 g. The cut surface revealed multiple solid and cystic tumors that varied in size from barely visible to 27 cm in diameter. Metastases were found in ten of the 23 dogs examined since 1979. All 23 dogs had numerous firm nodules in the skin and subcutis, and ten of 11 bitches had multiple uterine leiomyomas. Histological examination of the renal cortex showed multifocal hyperplastic to highly malignant epithelial proliferations. Skin lesions consisted of dense collagen fibers, and the uterine tumors consisted of interlacing bundles of smooth muscle cells. Pedigree analysis strongly indicates that the syndrome is hereditary, probably in an autosomal dominant pattern. This seems to be the first description of such a syndrome in domestic animals. Comparable syndromes in man are discussed.