The Cartwright (Yt) blood group system consists of two antigens, Yta and Ytb, that result from point mutations in the acetylcholinesterase gene on chromosome 7q. Yta is a high-incidence antigen, whereas its antithetical antigen, Ytb, shows much lower incidence. Anti-Yta and anti-Ytb are relatively rare. Anti-Yta is more commonly found in individuals of Jewish descent. Cartwright antibodies are rarely clinically significant; however, cases of in vivo hemolysis have been reported, suggesting that clinical significance should be interpreted on a case-by-case basis.