1. A case of hypophosphatasia in a boy who sustained a fractured left femur is described.

2. The literature is reviewed, and the reported cases are found to fall into severe, moderately severe and mild forms.

3. The diagnostic features of the disease are the radiological picture, which resembles that of rickets, very low serum alkaline phosphatase, and excessive phosphoethanolamine excretion in the urine.

4. Other clinical features may be a failure to thrive in early infancy, premature loss of deciduous teeth, hypercalcaemia and renal damage.

5. The function of alkaline phosphatase in bone metabolism in relation to this disease has been discussed.