Giant dermoid associated with foot duplication.

After resection at birth of an accessory left foot, a white male infant was followed up for a slowly enlarging posterior calf mass of the same leg. When the patient was 8 years old, the mass was thought to have enlarged sufficiently to warrant excisional biopsy. Histologic examination of the tumor was consistent with the diagnosis of a dermoid cyst, revealing a lesion lined with stratified squamous epithelium and containing cutaneous adnexal structures represented by eccrine sweat glands. A congenital dermoid in the extremities is unusual. The prognosis following removal is good, and recurrence is rare.