Summary. Hypophosphatasia is a rare metabolic bone disease characterised by defective bone and teeth mineralisation owing to reduced activity of tissue nonspecific alkaline phosphatase due to mutation in ALPL (TNSALP) gene. Seven clini- cal forms of HP have been described. The severity and the clinical course of hypophosphatasia are highly variable, ranging from intrauterine death to premature loss of teeth only. We report on two affected girls with hypophosphatasia and spontane- ous improvement of skeletal defects. The first patient is a four-year-old girl with perinatal nonlethal form of the disease. From another family is the 15 year-old-girl, with typical clinical and radiological features of childhood hypophosphatasia. The diagnosis was based on clinical course, radiological findings, low serum alkaline phosphatase activity in patients and their parents, and later confirmed by the molecular analysis of the ALPL gene. We have described in more detail the clinical manifestations and radiological findings relevant for the recognition of hypophosphatasia, because the disorder is rare, clini- cal presentation heterogeneous and the recognition rate poor.