Primary gastric lymphomas are exceptionally rare gastrointestinal cancers in children [1,2]. Central nervous system involvement at the time of diagnosis is not uncommon, but there are no published reports of primary gastric lymphoma involving cavernous sinus (CS) during treatment [3,4]. We report a case of primary gastric lymphoma in a previously healthy 13-year-old boy that developed CS involvement after the second cycle of chemotherapy. He presented with a 1-month history of epigastric pain, and several episodes of hematemesis and melena. He lost 3 kg during the previous month. At presentation he looked ill, with pale conjunctiva. Physical examination showed a palpable mass in the left upper abdominal quadrant. Abdominal tomography showed diffuse thickening of the gastric rugae involving the entire fundus, a 33-mm diameter mass over the splenic vein in the corpus, and pancreatic invasion. Upper gastrointestinal endoscopy was performed and a round ulcer 3 cm in diameter was noted in the body of the stomach. The mass was diagnosed as diffuse large B-cell NHL (CD20 positive) associated with Helicobacter pylori gastritis, based on examination of the biopsy specimen. Neoplastic cells were strongly positive for CD20 and negative for cytokeratin, desmin, CD79a, S100, and CD99. The Ki67 proliferative index was 99%. EBV serology was negative. Written informed consent was obtained from the patient.The patient was treated for the H. pylori infection using a proton pump inhibitor combined with clarithromycin and amoxicillin. Computed tomography of the chest, cranial MRI, and bone scintigraphy were normal. Bone marrow aspiration showed that there wasn't any malignant cell infiltration. He received 2 cycles of a chemotherapeutic regimen that included rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone. The initial cytologic status of CSF was normal; therefore, he did not initially receive intrathecal treatment.After the second chemotherapy cycle he presented with a 2-week history of headache and left