A 59-year-old woman's father and paternal grandmother died of colorectal cancer and her paternal uncle died of pancreatic cancer. She was positive for fecal occult blood and underwent colonoscopy. The colonoscopy revealed a type 0-Ⅱa+ Ⅱc lesion in the transverse colon suspected to be submucosal deep invasion, and the biopsy revealed poorly differentiated adenocarcinoma. Contrast-enhanced CT showed no regional lymphatic metastasis or distant metastasis. She was diagnosed with transverse colon cancer, T1N0M0, cStage Ⅰ, and laparoscopic partial colectomy and D2 lymphadenectomy were performed. Histopathological examinations showed medullary carcinoma, pT2(MP), Ly1a, V0, BD1, Pn1a, pPM0, pDM0, pN0. She had 2 of the items in the revised Bethesda Guideline, and was suspected of having Lynch syndrome(LS). There is no definitive diagnosis of LS because she did not want MSI or other genetic testing. However, the surveillance should be required not only for recurrence of colon cancer but also for occurrence of LS-related tumors.