Soft alveolar sarcoma is a rare tumor (0.5% to 1% of soft-tissue sarcomas) of poor prognosis that often affects the young subject, with a moderate male predominance. The authors present the diagnostic and therapeutic course of a 60-year-old patient from Niger with no particular previous history, consulted for a painless swelling of the right arm evolving for 6 months, in which the diagnosis of alveolar sarcoma of the soft parts of the arm was selected. A monobloc surgical excision decision was made, with the anatomy and function of the limb retained, with the filling of the area resected with cement and fixed by a locked nail. A conventional three-course chemotherapy regimen was instituted. Alveolar sarcoma of the soft tissues is a rare tumor whose imagery remains unclear, but the diagnosis is based on surgical excision with histopathological examination and immunohistochemical analysis.