The most common site of primary malignant melanoma is the skin, however, virtually any organ system may be involved. Metastatic melanoma of unknown primary origin accounts for approximately 2-6% of all melanoma cases. The mediastinum as the site for malignant melanoma is extremely rare, both as a primary or metastatic lesion. Primary malignant melanoma of mediastinum is very rare with only a handful of reports in the literature. We hereby report a rare case of malignant melanoma of mediastinum in a 31 year old male who was initially misdiagnosed on fine needle aspiration cytology as adenocarcinoma for which he received chemotherapy with clinical deterioration. Even on extensive meticulous search, no primary was discovered.