Trousseau's syndrome involves unexplained thrombotic events along with malignancy. We report the cases of 3 patients undergoing chemotherapy for gastric cancer in whom Trousseau's syndrome occurred. Case 1 involved a 43-year-old woman undergoing S-1/cisplatin( CDDP) combination therapy as first-line chemotherapy for type 4 remnant gastric cancer( cT4bN2M1P1/stage IV) who experienced left hemiplegia. Cerebral hemorrhage of the right parietal lobe was diagnosed by computed tomography( CT), and thrombosis from the upper sagittal sinus to the right sinus sigmoideus was diagnosed by magnetic resonance venography( MRV). Case 2 involved a 59-year-old man undergoing S-1/irinotecan (CPT-11) combination therapy as second-line chemotherapy for type 3 gastric cancer( cT3N1M0H1/stage IV) who experienced ataxic, stuttering, and left membrum inferius paralysis. Multiple cerebral infarction of the right parietal lobe was diagnosed by magnetic resonance imaging (MRI). Case 3 involved a 67-year-old woman undergoing S-1/CDDP combination therapy as preoperative chemotherapy for type 3 gastric cancer( cT4aN1M0/stage IIIA) who experienced right cerebellum incontinentia, nystagmus, and right facioplegia. Multiple cerebral infarction of the right cerebellum and pedunculus cerebellaris medius was diagnosed by MRI. An anticoagulant was administered orally for stroke, and chemotherapy for gastric cancer was resumed after activities of daily living( ADL) improved in all 3 patients. Recurrent stroke was not diagnosed in any of the 3 patients. Patients with malignancy often exhibit hypercoagulability associated with cancer. Accordingly, periodic blood tests for coagulation should be performed and dehydration should be prevented to prevent strokes in cancer patients.