Mesenchymal chondrosarcoma is a malignant neoplasm arising from cartilaginous bone or soft tissue. It is uncommon yet devastating. Our patient was a 21-year-old man who presented with pleuritic chest pain and weight loss. His chest radiograph showed left pleural effusion. His pleural effusion analysis was consistent with exudative pleural effusion. Tuberculosis workup was negative. Pleural fluid cytology did not yield malignant cells. Subsequently, his computed tomography of thorax showed left rib sclerotic lesion with soft tissue component. Biopsy of the soft tissue eventually confirmed the diagnosis of mesenchymal chondrosarcoma. He succumbed to his illness before the diagnosis was confirmed. We hope that through this case report, we are able to provide some insight into this rare condition.