Significant hypophosphatemia is commonly due to Vitamin D deficiency. Any sporadic onset of hypophosphatemia in adults warrants workup to identify alternate causes. Hypophosphatemia may also be the only manifestation of an occult malignancy. A high index of clinical suspicion can help diagnose such conditions in early stages. Prompt treatment of the cause can correct this biochemical abnormality. We describe a case report of a woman presenting with severe hypophosphatemia and osteomalacia, leading eventually to the diagnosis of a phosphaturic mesenchymal tumor of the temporo-occipital bone. Surgical resection of tumor led to normalization of the biochemical parameters as well as a complete clinical recovery.