The carpometacarpal boss is a bone prominence involving the carpometacarpal joints of the index and long fingers. Analysis of forty-seven patients possessing a total of fifty-seven lesions showed that direct trauma to the dorsum of the wrist as well as repeated mechanical stress to the wrist were implicated in the etiology of this deformity in most cases. Conservative treatment was all that was needed in all but sixteen lesions. When there was no specific history of injury, surgery was rarely needed, but surgical intervention frequently was required in those lesions when there was a definite history of trauma. Adequate excision of the lesion relieved the symptoms, and also removed the cosmetically unsightly deformity.