BackgroundIsolated mediastinal metastasis from a malignant tumor and small cell carcinoma of the bladder are both very rare.Case presentationA 76-year-old woman who had undergone surgery for bladder cancer twice was referred to our hospital for a right paracardiac mass noted in chest computed tomography findings, and resection of the tumor was performed. Histological analysis of the mediastinal tumor revealed it to be a metastatic small cell carcinoma of the bladder. At 4 months after surgery, multiple metastatic lesions were found in the chest and liver, and chemotherapy for small cell carcinoma was started.ConclusionsWe present this case of mediastinal metastasis of small cell carcinoma of the bladder, which is very rare, to show the importance of surgical resection of an isolated mediastinal tumor. Such a procedure should be considered, as histological diagnosis of the tumor could be useful for determining therapeutic options.