Primary mediastinal melanoma is extremely rare. The diagnosis is based on the presence of epithelioid cells with cytoplasmic melanin pigment in the histological study and a typical expression in immunohistochemical studies, and the exclusion of other primary sites of tumor. Clinical symptoms include cough, chest pain, shortness of breath, hemoptysis, dysphagia, and weight loss. The prognosis is usually unfavorable and there is no agreement on optimal therapy. Herein, we report a 49-year-old female patient with malignant melanoma presenting as a mediastinal mass without an extrathoracic primary.