The symptoms of XLH can vary in severity. Some people with XLH have no apparent bone-related symptoms and only hypophosphatemia, while others have severe symptoms. In many cases, symptoms become apparent within the first 18 months of life, when a child begins to bear weight on the legs. Early signs and symptoms may include abnormal bone development (leading to bowing or twisting of the lower legs) and short stature or a slowing growth rate. Other symptoms that may be present early or may develop include:

• Bone pain.
• Muscle pain and weakness.
• A waddling gait (manner of walking).
• Joint pain caused by hardening (calcification) of tendons and ligaments.
• Abnormal tooth development.
• Tooth abscesses and dental pain.
• Rickets that does not improve with traditional Vitamin D therapy.

In some cases, symptoms of XLH do not begin until adulthood. Symptoms that may develop in adults with XLH include joint pain and impaired mobility from enthesopathy (calcification of the tendons, ligaments, and joint capsules), tooth abscesses, and hearing loss.

XLH is diagnosed based on a physical exam, blood tests, imaging tests such as X-rays, and family history. Specific factors considered for the diagnosis include:

• A slow growth rate and noticeable bowing of the legs or other skeletal abnormalities.
• Low levels of phosphate and high levels of FGF23 in the blood.
• Lack of response of phosphate levels to vitamin D treatment.
• Phosphate wasting in the kidneys.

Genetic testing for XLH is available and may confirm the diagnosis if a mutation is identified, but it is not necessary for the diagnosis.

• Growth hormone to improve growth in children.
• Corrective surgery to fix bowed or bent legs.
• Treatment to repair skull abnormalities, such as premature fusion of the skull bones (synostosis).
• Dental procedures to treat pain in the teeth and gums.

XLH is a lifelong condition that may require ongoing treatment and monitoring. While some people with XLH may have only short stature and otherwise good health, there can be significant morbidity associated with XLH as people with the disease get older. This may result from mobility impairment, pain, and discomfort, which may be caused by various complications including osteoarthritis, problems with the tendons and ligaments (enthesopathy) or stress fractures in weakened bones (insufficiency fractures). Furthermore, problems can arise due to incorrect or inadequate treatment or misdiagnosis, since there is a lack of accessible treatment guidelines and awareness of XLH. Additional problems in some people may include:

• Loss of permanent teeth from recurrent dental abscesses.
• Spinal stenosis due to calcification of the spinal ligaments.
• Persistent lower-limb bowing and twisting (torsion) which can lead to misalignment of the legs, requiring surgery.
• Repeated surgeries for bone deformities or complications from previous surgeries.
• Prolonged healing times after surgeries, sometimes requiring several months of immobilization.
• The need for total hip and knee arthroplasty from degenerative joint disease and enthesopathy.
• Complications from medications - for example, phosphate treatment can cause an upset stomach and diarrhea.

While starting medical treatment very early in childhood can increase final adult height, it is not yet known whether (or how much) this can prevent later-onset complications, and additional (new) symptoms can develop during adulthood.