In a retrospective study of 42 consecutive Japanese patients with advanced colorectal cancer between April 2005 and December 2009 at Saitama Medical University Hospital and International Medical Center, genotyping revealed UGT1A1 in 24 patients, and UGT1A1-6/UGT1A1-28 in 18 patients. This evidence concerns the gene UGT1A1 and colorectal cancer.