A 69-year-old man underwent right hemicolectomy for colon cancer in the transverse colon in 2005. Two years after surgery, he was admitted with abdominal pain. Colonoscopy revealed a submucosal tumor of approximately 4 cm in size at the ileocolonic anastomosis site. In the biopsied samples from the anastomosis site, there was diffuse proliferation of large lymphoid cells, which were immunohistochemically positive for CD3 and CD4, but negative for CD8 and CD20. Clonality analysis of T-cell receptor-beta gene rearrangement revealed a single band, indicating monoclonal proliferation of the T- lymphocytes. Epstein-Barr virus in situ hybridization did not reveal any positive signals in any of the tumor cells. Anti-human T-lymphotropic virus-I was negative. Based on these findings, the recurrent tumor was diagnosed as peripheral T-cell lymphoma-unspecified (PTCL-u).