A 64-year-old man who was a smoker suddenly suffered from a weakness of the left 2nd finger to the 5th. T2-weighted magnetic resonance imagings of the brain demonstrated multiple-spotted and patchy shadows with a high signal intensity in the cerebral white matter and bilateral basal ganglion, indicating a diagnosis of cerebral infarction. Furthermore, a chest roentgenogram revealed a mass shadow in the right lower lung field, which was diagnosed as an adenocarcinoma based on the results of transbronchial curettage. Neither arteriosclerosis nor thrombus formation was found, despite the presence of hypercoagulation; therefore the patient was diagnosed as having Trousseau’s syndrome, secondary to a malignant tumor. Anticoagulation with heparin was administered by continuous intravenous infusion, and 10,000 units of heparin calcium were subsequently injected subcutaneously twice daily. The patient received several series of systemic chemotherapy regimens for lung cancer, but none was effective. Although the disease continued to worsen, no new neurological symptoms appeared. Cerebral infarction secondary to hypercoagulation induced by a malignant tumor has been recognized as Trousseau syndrome; however, few cases have been reported in association with lung cancer. The administration of heparin by subcutaneous injection successfully controlled the disease condition in the present case.