We report a 38-year-old mestizo man with the sudden onset of left upper abdominal pain while climbing Mt. Fuji, which is the highest mountain in Japan. Enhanced computed tomography showed splenic infarction. Although his peripheral blood smear was normal, a hemoglobin S level of 40% established the diagnosis of sickle cell trait (SCT). This trait is common worldwide, but is not well recognized by doctors in Japan because no Japanese patients with SCT have been reported. However, in Japan it is important to consider SCT when assessing foreign patients with splenic infarction.