To identify the outcomes of prognostic factors of solitary plasmacytoma mainly treated with local radiotherapy (FIT). The data were collected from 80 patients with solitary plasmacytoma (SP). Forty patients (50.0%) received radiotherapy (FIT) alone while 38 of them (47.5%) were treated with surgery (S) and FIT. The median radiation dose was 46 Gy (range 30-64). The median follow up was 2.41 years (range 0.33-12.33). Ten-year overall survival (OS) and local relapse-free survival (LRFS) were 73% and 94%, respectively. The median progression-free survival (PFS) and multiple myeloma-free survival (MMFS) were 3.5 years and 4.8 years, respectively. On multivariate analyses, the favorable factors were radiotherapy dose of >= 50 Gy and RT + S for PFS and younger age for MMFS. For the patients with medullary plasmacytoma, the favorable factor was younger age for MMFS. RT at >= 50 Gy and RT + S may be favorable prognostic factors on PFS. Younger patients, especially with head-neck lesion and without pre-RT macroscopic tumor, seem to have the best outcome when treated with RT +/- S. Progression to MM remains as the main problem especially for older patients.