Human Glycoprotein A33 (GPA33) is a single-pass type I membrane protein, belongs to the CTX family of cell adhesion molecular within the immunoglobulin family, can be expressed in normal gastrointestinal epithelium and in 95% of colon cancers. GPA33 consists of one Ig-like C2-type domain and one Ig-like V-type domain. The predicted mature protein includes a single transmembrane domain, a extracellular region and a intracellular tail. Intracellular traffic and recycling to the cell surface appear to play an important role in GPA33 function and to have an influence on its surface density superseding translation regulation. GPA33 has become a promising target of immunologic therapy strategies. GPA33 may also play a important role in cell-cell recognition and signaling.