Hypoparathyroidism is a disease characterized by hypocalcemia and hyperphosphatemia derived from deficient actions of parathyroid hormone (PTH). We report the case of 43-year-old Japanese man with PTH-deficient hypoparathyroidism introduced to an endocrinologist in our hospital. As he had complained of hearing disturbance since the age of 20, we decided to investigate the GATA3 gene. Direct sequencing of PCR products identified a novel heterozygous mutation, 432insG, in the GATA3 gene. The mutation introduces a premature stop codon at exon 4 (K302X), which results in a loss of both zinc finger domains of the GATA3 protein. However, because the mutation in the GATA3 gene found in this patient is highly likely to impair GATA3 function, we speculate that it is extremely unlikely that this patient has mutations in other genes that cause PTH-deficient hypoparathyroidism, in addition to the GATA3 mutation described here.