Synthesis and degradation of collagen is an essential component of wound healing. In most persons, this deposition of collagen results in the formation of a fine line scar which restores much of the tensile strength to the injured tissue and is cosmetically acceptable. However, in certain individuals, the result of wound healing is the excessive accumulation of collagen, resulting in a hypertrophic scar or keloid. The precise origin of this abnormal collagen deposition is unknown, but recent studies have begun to identify potential mechanisms for these disfiguring and painful lesions. This article will review the clinical and laboratory findings pertinent to understanding the origin and treatment of excessive scarring.