The basal-cell nevus is a dysgenetic dermatosis characterized by multiple small cutaneous tumors. These are histologically indistinguishable from basal-cell cancer. Malignant supervention is common, generally resulting in multiple basal-cell cancers of the face in young adults. Developmental defects of other systems are often present. Incidence seems to be based on an inherited, sometimes familial, predisposition. Clinical Features Basal-cell nevi may appear at birth or be first noted in infancy. Occasionally the lesions may begin at about puberty and gradually increase in number and in size over a period of years. There may be few or hundreds, and there is a tendency for bilateral distribution, but this need not be symmetrical. The size of the individual lesion varies from that of a pinhead to approximately 5 mm. in diameter. Pedunculated and papular lesions are common on the neck, eyelids, and axillae. The color is