Tumor-induced or oncogenous osteomalacia is a rare paraneoplastic syndrome characterized by osteomalacia with hypophosphatemia, hyperphosphaturia, and undetectable or inappropriately low circulating concentrations of 1,25-dihydroxyvitamin D3. The syndrome is associated with the presence of a tumor whose successful removal leads to clinical and biochemical cure. More than 80 cases of tumor-induced osteomalacia have been reported, but recognition of affected persons is still frequently delayed or neglected. This has been due, in part, to difficulty in locating the tumors that cause the disorder, but it may also be the result of inappropriate assessment of the cause of hypophosphatemia. Progress in identifying the pathophysiology of tumor-related osteomalacia has therefore been limited. However, there may be homologies between tumor-related osteomalacia and inherited hypophosphatemia. Studies of the latter, which are included in this review, may help to elucidate the factor or factors that cause tumor-induced osteomalacia.