Trichoepitheliomas are benign cutaneous tumors that originate from hair follicles and present in two clinical forms. Multiple trichoepithelioma has autosomal transmission and is dominant as a result of the loss of heterozygosity in the 9p21 region, whereas the giant form is solitary, nonhereditary, and rarely affects the perianal region. Diagnostic differentiation from basal cell carcinoma presents notable difficulty, and the use of immunohistochemical studies often is necessary for correct differentiation. The concomitant presence of giant solitary trichoepithelioma and basal cell carcinoma raises the question of whether there is the possibility of malignant transformation, or if it is simply an encounter between the two types of neoplasia. The objective of the present study was to report on a patient who had the two clinical forms of trichoepithelioma (multiple trichoepithelioma and giant solitary trichoepithelioma) in the perianal region, without hereditary antecedents. In this case, the transformation of the largest-sized lesion into basal cell carcinoma was observed. The lesions were studied by means of histopathologic and immunohistochemical studies to investigate the bcl-2 oncogene. The tissue expression characteristics for bcl-2 and the histopathologic examination allowed the diagnosis of multiple trichoepithelioma in the smaller lesions and nonsolitary giant trichoepithelioma with malignant transformation into basal cell carcinoma in the largest-sized lesion. After surgical excision and adjuvant radiotherapy, the patient is now asymptomatic, without signs of relapse, eight months after the surgery.