A 69-year-old male with cT4N2M0 stage IIIB primary lung adenocarcinoma revealed progressive anemia and thrombocytopenia while receiving cancer treatment. Although drug-induced and carcinoma bone-marrow invasion were considered as a differential diagnosis, we concluded that his diagnosis was idiopathic thrombocytopenic purpura (ITP) because of elevating platelet-associated immunoglobulin G (215 ng/10⁷ cells) and distinctive results for bone-marrow biopsy. Moreover, the infection of Helicobacter pylori (HP)was ascertained, and a complication of his gastric ulcer was revealed. Lung cancer with immune thrombocytopenic purpura such as ITP and ITP-like syndrome is a rare clinical event, and only 11 cases have been reported in Japan. Although 2 of the 11 were complicated by a gastric ulcer, it is difficult to differentiate other illnesses if the patient is complicated by having both of them. A relationship between ITP and HP has recently been reported. Because this bacterium is one of the causes of gastric ulcers, we consider it necessary to have gastric problems in mind if the cancer patients are complicated with ITP. We report a case along with a brief review of the literature and summarize the 11 cases that have been reported in Japan.