Sclerotic fibroma of the skin is a hardened, fiber-like skin tumor, characterized by wasting of the epidermis, the outer skin layer, and formation of round or oval fibromas in the dermis, the inner skin layer. The fibromas are composed of collagen, the fiber-like protein of connective tissue, arranged in whorls and separated by clefts containing mucin, a protein found in mucus. The fibroma is distinct and surrounded by normal collagen. Sclerotic fibroma of the skin is associated only with fiber-like tissue development and no changes in nerve or muscle. This condition was first described in association with Cowden's disease, a birth-related condition characterized by a slowly growing mass of abnormal tissue in multiple sites. However, another case was reported in which the same fibroma occurred in the absence of Cowden's disease. A case is described of a 44-year-old man with a node-like lesion on his right forearm, which had been present for 20 years. Tissue microscopic examination of the lesion revealed an oval-shaped area of growth of fibrous tissue. There was no evidence of membrane or capsule, thick bands of collagen were arranged in an unusual pattern, and elastic fibers were absent. (Consumer Summary produced by Reliance Medical Information, Inc.)