Since the international gastric cancer linkage consortium first proposed screening criteria for the detection of CDH1 germline mutations in hereditary diffuse gastric cancer(HDGC), the low yields of previous attempts to identify patients with HDGC in Japan, where gastric cancer is endemic and mass screenings for it have been established, have made clinicians less enthusiastic about pursuing the genetic etiology of the peculiar occurrence of gastric cancer. A report published in 2011 described a case with a typical truncated mutation of CDH1 and another with an exon 3 deletion of this gene. These findings have rekindled the curiosity of practicians and pathologists confronted with unusual gastric cancers of various types such as younger- onset, familial clustering, or the exhibition of a specific characteristic morphology. The status and history of the investigation of the genetic backgrounds of Japanese gastric cancers are reviewed, and the pathological features of the Japanese cases of HDGC are described.