A hyperpigmented perianal nodule.

Basal cell carcinoma (BCC) is the most common cutaneous malignancy. Ultraviolet light is an important risk factor for the pathogenesis of BCCs; the vast majority are found in sun-exposed areas. BCCs occurring in the perianal or genital regions are seldom seen. Less than 1% of all BCCs occur at these sites. Etiologic factors other than solar exposure must be taken into account for such cases. We report a rare case of BCC that was initially detected during a routine colonoscopy.