Follicular lymphoma (FL) is an indolent lymphoma that often transforms into a high-grade lymphoma, mostly diffuse large B-cell lymphoma. A case of FL suggested to transform into plasmablastic lymphoma is presented. A 59-year-old man was admitted to our hospital because of right lower abdominal pain and vomiting. Computed tomography showed a mass in the ileocecum. Colonoscopy showed a mass with an ulcer in the ascending colon, and surgery was performed. Immunohistochemical staining of the biopsied mass showed infiltrated lymphocytes that were positive for CD38, CD45, CD138, and λ chain, and negative for CD4, CD5, CD8, CD10, CD20, CD56, and κ chain. Flow cytometric analysis of the ascites showed similar results. FISH analyses performed using lymph node biopsy specimens, ascite fluid and pleural effusion fluid identified the presence of an IGH/BCL2 translocation. FL was suggested to transform into PBL. Although the patient received three courses of R-CHOP chemotherapy and salvage chemotherapy, the patient died because of lymphoma progression less than 6 months after the diagnosis of PBL. Transformation of FL to PBL is highly unusual. The lack of a standard treatment for PBL results in the poor outcome of this entity. Novel therapeutic approaches are needed.