PTHrP has had an unidentified role in medicine since 1930, when Albright described a patient with renal cortical cell carcinoma with hypercalcemia. Since then hypercalcemia has been recognized as the most common paraneoplastic syndrome. At that time the concept of "ectopic PTH syndrome" was introduced, and remained in literature until the true etiology was finally described. In the early 1970's Roof and Benson presented evidence that PTH in humoral hypercalcemia differed from "authentic" PTH. This marked the starting point for researchers to try identifying the molecule that mimicked PTH action and structure. This molecule, named parathyroid-related peptide, has been associated to hypercalcemia seen with solid tumors, such as squamous cell carcinoma of the lung and renal cortical cell carcinoma. PTHrP has been demonstrated to have similar actions to PTH but to differ in decreasing osteoblastic activity while increasing osteoclastic activity. The more fascinating finding was the presence of the PTHrP genes throughout the body, mostly the lactating breast as well as the heart, lungs and skin among others. Despite its identification, finding its physiological roles on normal tissue still remains to be clarified.