Solitary plasmacytoma is an uncommon hematologic malignancy characterized by the monoclonal proliferation of abnormal plasma cells in the bone or extramedullary tissues and the absence of other multiple myeloma-defining clinical characteristics. Mostly, solitary extramedullary plasmacytoma (SEP) occurs in the head and neck region, also called solitary extramedullary plasmacytoma of the head and neck (SEPHN). Although the standard of care for SEPHN is not well established, either a surgical approach or localized external beam radiotherapy (EBRT) can be used as a definitive treatment. Due to the high radiosensitivity of SEPHN, EBRT has been associated with adequate therapeutic effects in the management of SEP, with the advantage of being a noninvasive modality that yields high rates of local control with a reasonable toxicity profile. We present a case series of three patients with SEPHN treated with EBRT at our institution with clinical outcomes.