Whereas basal cell carcinoma usually is a slow-growing tumor of the head and neck region, we have observed, over a 20-year period, three large, unique basal cell tumors of the back that were distinctive and presented clinical and histologic problems in diagnosis. They commonly formed exophytic, vegetative, flesh-colored to red, sessile plaques up to 20 cm in diameter. Ulceration was the principal feature of a fourth tumor, which destroyed the skin of the entire lumbar area and invaded the muscle. Regional-node metastases from this tumor showed basal cell carcinoma. Histologically, all the primary lesions were adenoid basal cell carcinomas with mucinous stroma. Histochemistry in two cases demonstrated minimal respiratory enzymes and no special esterolytic or lysosomal enzymes. Surgery was curative in three of these cases of rare, giant variant of basal cell carcinoma of the skin.