The fibromatoses are a heterogeneous group of disorders characterized by proliferation of fibroblasts. Infantile myofibromatosis is a variant that is distinctive because of its multicentric origin, appearance at birth, and cellular composition, which is predominantly myofibroblasts. We treated a patient with infantile myofibromatosis with the interesting clinical presentation of a linear lesion involving the left arm and shoulder, and aggressive hepatomegaly with jaundice secondary to fibroblastic infiltration of the common bile duct and gallbladder. Diagnosis was confirmed histologically and ultrastructurally. Excision of the cutaneous lesion was facilitated by tissue expansion of uninvolved regional tissue.