The impact of different treatment modalities and prognostic factors on the clinical course of primary thyroid diffuse large B-cell lymphoma (PTDLBCL) is still the subject of research. This study was conducted to clarify these clinical aspects of this disorder. The clinical parameters of 48 patients with PTDLBCL at time of diagnosis were comparable to those of previous studies. Patients underwent either radiotherapy (RT) ± surgery (SX), chemotherapy (CHT) alone or in combination with local treatments (RT or SX), or SX followed by CHT and RT. A 90% complete remission (CR) rate was observed among patients who underwent combined treatment modalities (CTM), compared to 76% among the others. The 5-year progression-free survival differed significantly between both groups (p = 0.028). Poor performance status and advanced age correlated with decreased survival. PTDLBCL is a curable disease prevalent in elderly patients. Combined treatment modalities were able to induce an elevated rate of CR, improving long-term survival in younger patients. However, the outcome in elderly patients still remains unsatisfactory.