Clinical, histopathologic and electronmicroscopic findings in a case of congenital localized multiple fibromatosis of interscapular region are presented. This 10 year-old Japanese girl developed this lesion since she was 3 weeks old, metastases have never been observed. The histological and electron-microscopic features point to the hamartomous origin of this tumor with partial differentiation of its cells towards myofibroblasts and atypical fibroblasts. The differential diagnosis from other soft tissue tumors in infancy and early childhood is discussed.