Subcutaneous fat necrosis (SCFN) is a rare, self-limited and benign disorder that develops after birth. A 3-month-old-boy presented with a semi-mobile mass under the skin without erythema on the left inguinal area. Ultrasound (US) revealed a mass within the subcutaneous fat layer over the left internal oblique and the sartorius muscles with heterogenous echogenicity. Computed tomograpy (CT) showed that the mass had a smooth border with partially spicular extensions to the subcutaneous fat. The presumptive diagnosis was rhabdomyosarcoma. Surgical exploration and excision biopsy were performed. The pathological examination revealed SCFN.