A 42-year-old man presented with dyspnea, left-sided chest pain and sudden onset of hair loss. Multiple pleural masses were found on computed tomographic scans which were highly suggestiveof malignant pleural mesothelioma or pleural metastases. After open pleural biopsy, pathological examination showed the lesion to be a metastatic pleural thymoma or primary pleural thymoma with an exceptional localization. Clinical signs and symptoms of myasthenia gravis (MG) were absent and anti-acetylcholine -receptor antibodies were in normal range. Electromyogram was normal. PET-CT showed anterior-superior hypermetabolic partially calcified mass (malignant thymoma, SUV: 4-4. 2) located to the thymus. The patient was diagnosed as alopecia areata (AA) in the view of dermatological findings. Association of AA and thymoma was previously reported in the presence of MG as individual cases. Nevertheless, this case represents an unusual form of metastatic thymoma with diffuse pleural dissemination mimicking malignant mesothelioma associated with AA, but not accompanied by MG. It should be emphasized that dermatologists must be aware of the clinical findings of a pulmonary disease such as thymoma in patients with AA.