The outcomes of patients with stage IV thymoma are derived largely from small patient cohort studies from single institutions. Although surgery is a pillar in the management of early-stage and locally advanced thymoma, resection is more controversial for patients with stage IVA thymoma. Using a large national population database, we set out to define the long-term outcomes of patients treated surgically and nonsurgically for stage IV thymoma. The Surveillance, Epidemiology, and End Results (SEER) database was examined to identify patients with stage IV thymoma (SEER historic stage IV with extension by discontinuous metastases) between 1988 and 2010. By this definition, stage IV included both stage IVA and stage IVB diseases. Surgical management was defined by grouping SEER categories of “radical surgery,” “debulking surgery,” “total surgical removal,” “simple or partial removal,” “surgery not otherwise specified,” “local tumor excision,” and “surgery of regional, distant site.” Nonsurgical management was defined by “no surgery,” “excisional biopsy,” and “incisional biopsy.” Overall survival (OS) and cancer-specific survival (CSS) were calculated from the time of diagnosis with KaplanMeier methods and compared with log-rank tests. For those managed surgically, age, sex, race, radiotherapy, type of procedure, and World Health Organization histology were investigated as prognostic factors with Cox proportional hazard models. P values were considered significant if o0.05. Overall, 110 patients (39.0%) underwent surgical resection and 172 (61.0%) were managed nonsurgically for stage IV thymoma (Table). The follow-up