The pathologic specimens from forty-seven patients with fifty-one recurrent basal cell carcinomas referred for Mohs' surgery were studied. Specimens from the original tumor and from each subsequent recurrence were reviewed. Of the original tumors, 65% demonstrated an aggressive* histologic picture characterized by poor palisading and an infiltrating and/or micronodular pattern. In twelve cases the recurrent tumor developed a more aggressive histologic picture, but in seven cases the histologic picture became more benign. Electrodesiccation and curettage was the initial treatment for forty-one basal cell carcinomas. Ten tumors had been excised previously, with routine pathologic examination indicating tumor-free margins in six of these lesions. It can be concluded that many recurrent basal cell carcinomas are aggressive from the beginning, and this often can be predicted from the histologic picture. Lesions with an aggressive pathologic picture should not be managed by blind technics such as electrodesiccation and curettage and may defy routine pathologic examination of conventional excision specimens. Mohs' surgery appears to be the treatment of choice for such lesions.