Primary extraosseous plasmacytoma (PEP) is a rare and localized form of plasmacytoma that is not well understood. This study aimed to investigate the clinical features and prognostic factors associated with PEP. Using the Surveillance, Epidemiology, and End Results (SEER) database, a total of 1044 patients diagnosed with PEP between 2000 and 2019 were identified. The average age was 60.3 & PLUSMN; 15.2 years, with 64.3% being male (male: female = 1.8:1) and 53.8% being over 60-year old. The survival outcome of patients with PEP depends on several factors including age, race, marital status, and treatment options such as chemotherapy, radiotherapy, and surgery, which were also identified as independent predictors of overall survival for PEP. Patients who were younger, Asian or Pacific Islander, American Indian or Native American, and received radiotherapy or surgery had a more favorable prognosis, while those who underwent chemotherapy had poorer outcomes.