Since its discovery in granulation tissue of healing wounds, now over a quarter of a century ago [22], the myofibroblast has been described in: (1) normal tissue; (2) diverse responses to injury and repair phenomena; (3) quasi-neoplastic proliferative conditions; (4) the stromal response to certain forms of neoplasia; and (5) benign and malignant neoplasms (for review [49]). In practical terms, the surgical pathologist is a daily witness to this panoply of myofibroblastic proliferation. An appropriate evaluation of the myofibroblast with regard to neoplasia is impossible without identifying briefly where these cells occur, and without defining this unique cell.