In this case, a young male patient diagnosed as hypophosphatemic osteomalacia and ankylosing spondylitis (AS) will be assessed by literature. A 32-year-old male patient who had been previously diagnosed as ankylosing spondylitis and hypophosphatemic osteomalacia was admitted to our clinic. In the beginning of the disease, he complained of pain on the first metatarsal bone and low back. Sacroiliac magnetic resonance (MR) images were interpreted as sacroiliitis. He was diagnosed as AS, and referred to many hospitals and received several therapies. He did not benefit from the treatment and his complaints worsened. The human leukocyte antigen (HLA) B-27 test was negative and alkaline phosphatase level was high. Old femur fractures were reported in the whole body bone scintigraphy. In addition, the patient was diagnosed with osteomalacia. While the patient was receiving vitamin D, oral phosphate, anti-tumor necrosis factor therapy was added. Patient's diagnosis was reevaluated. His final diagnosis was hypophosphatemic osteomalacia instead of ankylosing spondylitis.