Transient hyperphosphatasemia of infancy and early childhood (THI) is characterized by transiently increased serum activity of alkaline phosphatase (S-ALP), predominantly its bone or liver isoform, in children under five years of age. There are no signs of metabolic bone disease or hepatopathy corresponding with the increased SALP, nor is there a disease common to all children with THI. To date, THI has been reported in more than 400 children. Viral etiology of THI has been proposed; transiently increased bone turnover and impaired clearance of ALP from the serum were originally considered as its causes. The pathogenesis is most probably multifactorial. THI is a benign disorder, as prospective follow-up of children with a history of TH revealed normal growth and normal bone density. Children with TH should be spared from excessive diagnostic procedures.