Gastric cancer associated with pregnancy is extremely rare and the prognosis is generally grave. A 31-year-old Japanese women, 41 weeks pregnant, displayed disseminated intravascular coagulation (DIC), although clinical symptoms and diagnostic examinations did not indicate an obstetrical cause. She went into labor spontaneously and vaginally delivered a 3248-g normal female infant, after receiving a blood transfusion. On the day 5 postpartum, a gastroduodenal fiberscope examination indicated advanced gastric cancer. She was also diagnosed with bilateral chronic subdural hematoma and underwent an operation to allow drainage. It was not possible to treat her curatively, so she was treated conservatively for DIC. She died on day 13 postpartum. Necropsy of the iliac bone indicated bone marrow metastasis of adenocarcinoma. This is the first known case of a pregnant woman with DIC occurring as the first manifestation of advanced gastric cancer.