New clinical criteria for hereditary nonpolyposis colorectal cancer (HNPCC) that includes extracolonic cancers were recently proposed. We present 2 endometrial cancer patients who met the new criteria of 161 endometrial cancer patients.,Case 1: A 55-year-old female was operated on for synchronous double primary cancers of the endometrium and rectum. She had also undergone an operation for metachronous ascending colon cancer at the age of 44. She had five relatives with a history of colorectal cancer. The rectal cancer tissue revealed no microsatellite instability (MSI). Case 2: A 48-year-old female underwent a radical operation for synchronous double primary cancers of the endometrium and ovaries. She had three relatives with a history of colorectal cancer. The endometrial cancer tissue showed high MSI.,The frequency of endometrial cancer patients meeting the new HNPCC criteria was 1.2% (2/161). These are the first case reports selected from consecutive endometrial cancer patients.