The clinical and pathologic features of 61 cases of congenital and infantile myofibromatosis are presented. The tumor affected almost exclusively infants and young children; 88% of cases occurred before the age of two years, and 60% were noted at birth or shortly thereafter. Solitary (45 cases) and multicentric (16 cases) forms of the tumor could be distinguished; the solitary form was more common in males (69%) and affected chiefly the soft tissues of the head-neck region and the trunk. The multicentric form, on the other hand, predominated in females (63%) and was found not only in soft tissues but also in bones and viscera. Fourteen of the 16 cases with multicentric lesions were present at birth, and four of them had evidence of visceral involvement. Among the 16 cases were two sets of siblings, both brother and sister. Grossly, nearly all of the tumors were well demarcated; they measured from 0.5 to 7 cm in greatest diameter. Microscopically, they formed well-circumscribed nodules consisting of short bundles of plump, spindle-shaped cells displaying staining characteristics intermediate between fibroblasts and smooth muscle cells. Necrosis or a hemangiopericytoma-like pattern was often found in the center of the tumor nodules. Intravascular growth was encountered in several instances, but this feature did not seem to affect the clinical behavior. Of the 43 patients with follow-up data (mean-follow up 5.1 years), 36 were alive and well. Of the solitary lesions, three recurred. Of the multicentric lesions, five of the 15 patients showed evidence of spontaneous regression of both soft tissue and bone lesions. Four died, three of extensive involvement of multiple viscera, especially the lung, and one of "crib-death."