BACKGROUND Infantile fibrosarcoma (IFS) is a rare tumor. The highest prevalence is in the first 2 years of life. Cases typically manifest in the extremities, with rapid initial growth, are non-tender, and are a poorly delimited masses that vary in size or consistency and lack sensitivity. The treatment for IFS is a multimodal approach, and surgical excision has become the main treatment. This report aims to present the results of our work on IFS cases. CASE REPORT A 4-year-old girl was admitted to our hospital with a chief concern of a mass in the right lower leg that first appeared 3 years ago. Physical examination showed a single mass with dense-rubbery consistency, tenderness, and limited range of motion. Plain radiography was performed, and a soft-tissue mass was seen on the anterior 1/3 distal cruris of the right side. CT angiography showed a bulging soft-tissue mass, solid (38 HU), with size ±2.8×3.1×4.7 cm. MRI examination revealed an aggressive superficial soft-tissue mass in the cutaneous-subcutaneous compartment. Biopsy and immunohistochemistry were performed, and the results were consistent with IFS. A local excision was made to assess for pathological anatomy. CONCLUSIONS Infantile fibrosarcoma (IFS) is an uncommon tumor in early childhood. It tends to mimic other tumors, which may interfere with the correct diagnosis, which may contribute to its rarity. Local excision is the first treatment choice, with a good prognosis for IFS.