Transient hyperphosphatasaemia in infancy and childhood is a temporary and isolated elevation of serum alkaline phosphatase activity occurring without an obvious cause during the first years of life. The key to rapid and reliable diagnosis is the demonstration of a characteristic alkaline phosphatase isoenzyme pattern on zonal electrophoresis. The aim of this study was to analyse some clinical and biochemical features in the largest series of cases which has been ever identified in one hospital. Over a period of eight years (1992–1999), transient hyperphosphatasaemia of infancy and childhood was detected incidentally in 194 pat ients (106 boys and 88 girls, including 5 sibling pairs). Children presented with a wide variety of clinical disorders. Typical age predilection was proved (range 4 – 126, median 15 months). Marked seasonal clustering of cases from September to November (43% cases) was observed. The „epidemic“ incidence and familial occurrence supported strongly the idea of an infectious origin of the syndrome. Peak alkaline phosphatase activities varied in children from slightly to excessively elevated values and returned to normal spontaneously within several weeks. The high frequency of affected children (33%) among all patients under five years of age where alkaline phosphatase isoenzyme examination was requested by the physician suggests that this strange benign phenomenon cannot be regarded as a rare finding.

        Key words: transient hyperphosphatasaemia, childhood, alkaline phosphatase, isoenzymes, incidence.