Background: Ischemic stroke can occur in patients with an underlying or undiagnosed malignancy. We aim to report the clinical features of ischemic stroke patients in whom a previously undiagnosed cancer was detected after stroke onset. Methods: Clinical and laboratory records of 28 consecutive ischemic stroke patients with cancer were reviewed retrospectively. The analysis was made focused on the differences between patients who were already diagnosed as having cancer before ischemic stroke (Group A) and those in whom a previously undiagnosed cancer was detected after ischemic stroke onset (Group B). Results: There were 18 patients in the Group A and 10 in the Group B. In Group B patients, the indicators that led to the detection of cancer were as follows: ascites (n=2), liver enzyme elevation (n=2), anemia (n=2), hematemesis (n=1), hematochezia (n=1), and sore throat (n=1), and autopsy (n=1). Nine of the 10 patients (90%) in Group B, and 6 of the 18 (33%) in Group A had a gastrointestinal cancer. In Group B, 8 of the 9 patients showed elevated serum carcinoembryonic antigen (CEA) and/or carbohydrate antigen 19-9 (CA19-9). Stroke relapse, prognosis, diffusion-weighted imaging patterns and laboratory fi ndings were not different between the 2 groups. Conclusions: Gastrointestinal cancer was frequent in ischemic stroke patients with newly diagnosed malignancy after stroke onset in this study among Japanese patients. Physicians should be aware that underlying cancer may be present particularly in ischemic stroke patients whose stroke etiology is unclear or who have anemia or liver dysfunction. In such cases, measurements of CEA and CA19-9 levels are easy and useful screening for the detection of occult malignancies.