Primary splenic diffuse large B-cell lymphoma (DLBCL) is a rare clinical condition, which is generally treated by six to eight cycles of chemotherapy involving a combination of rituximab and the cyclophosphamide, adriamycin, vincristine, and prednisolone (CHOP) regimen. However, the treatment for chemorefractory primary splenic DLBCL remains controversial. Therapeutic splenic irradiation (SI) might be a reasonable and possibly the only treatment option with curative intention for patients with chemorefractory primary splenic DLBCL. However, the efficacy and safety of therapeutic SI are unclear. Herein, we present the case of a primary splenic DLBCL patient who was refractory to multiple chemotherapy regimens but achieved complete remission after administration of therapeutic SI. However, his condition was complicated with severe gastric variceal bleeding due to splenic venous thrombosis, which was successfully treated via splenectomy and short gastric vein ligation. On the basis of our findings, we concluded that the splenic venous thrombosis-induced gastric variceal bleeding was a rare but life-threatening adverse effect of the therapeutic SI administered for primary splenic DLBCL. Surgical intervention involving splenectomy and short gastric vein ligation is mandatory and should be performed as soon as possible for such patients.