We report 5 cases of infantile fibrosarcoma (4 boys and 1 girl) whose average age was 5, 7 months (range 0 days to 14 months). The tumor was congenital in 4 cases. All tumors presented in the extremities (forearm, hand, thigh: 1 case, lower leg: 2 cases). Treatment was based on surgery (3 cases: amputation, 2 cases: local excision) with a favorable course in all cases, even those with marginal excision (follow-up ranging from 5 to 21 years). The lesions were characterized by dense monotonous cells growing in a fascicular pattern, with small necrotic areas and scattered lymphocytes. The mitotic index was high (average 8/10 high-power fields). ETV6-NK3 chimeric RNA was detected by reverse transcriptase polymerase chain reaction in two cases out four cases from paraffin-embedded tissue blocks. The infantile fibrosarcoma is a good prognosis tumor characterized by particular histological features and ETV6-NK3 gene fusion.