Mediastinal and pleural metastasis of prostate cancer is very rare. To our knowledge, there have been no reported cases of prostate cancer associated with mediastinal metastasis and pleural seeding nodules. We report a histopathologically confirmed case of mediastinal and pleural metastasis originating from prostate cancer by biopsy, which on initial diagnosis, was suspected as being a malignant thymic tumor with pleural metastasis