A novel mutation of the claudin 16 gene in familial hypomagnesemia with hypercalciuria and nephrocalcinosis mimicking rickets: Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FH HNC) is caused by a mutation in the gene CLDN16, which encodes paracellin 1 (claudin-16), a tight junction protein mediating paracellular transport which is expressed in the thick ascending loop of Henle and in the distal convoluted tubule, where reabsorption of magnesium occurs. We present a 4 years old Turkish female child with a chief complaint of hypocalcemic tetany. A diagnosis of FHHNC was confirmed by genetic testing for a mutation in claudin 16 gene. Claudin 16 gene revealed homozygosity for the p.K183E(AAA>GAA) C.547A>G indicating the diagnosis of hypomagnesemia with hypercalciuria and nephrocalcinosis. To our knowledge, this is the first case of FHHNC reported in Turkish population diagnosed at molecular level.