XLH (short for X-Linked Hypophosphatemia) is a rare genetic disorder affecting 1 in 20,000 people worldwide causing rickets in children and osteomalacia in adults. It is still known by some as Vitamin D Resistant Rickets and is sometimes referred to as Familial Hypophosphatemia. This disorder can be passed down through families on a defective dominant X-Linked gene called PHEX, but new families can be affected as well due to spontaneous genetic mutations upon conception. The XLH Network began in 1996, incorporated as a not-for-profit corporation in 2005, and is now a 501(c)(3) charity. The organization provides both a public and a members-only website and a listserv discussion group for affected members. Very few physicians are familiar with XLH and without a physician experienced in its treatment it often goes undiagnosed, misdiagnosed, and/or inappropriately treated. The XLH Network aims to raise awareness about this little understood condition.