We report here on a girl and her father with HDR syndrome (Hypoparathyroidism, sensorineural Deafness and Renal anomaly syndrome). The proband, an 11 year-old girl, complained of periodic tetany lasting for 6 years, and also used a hearing aid because of sensorineural hearing impairment. Furthermore, she had hemimegalencephaly, and had been taking an anti-epileptic agent to treat psychomotor seizures for 6 years. Endocrine assessment showed modest hypocalcemia, hyperphosphatemia and hypophosphaturia with lower normal parathyroid hormone concentration, and she had no renal abnormalities. Her father, who was 40 years old at the time of the investigation, had sensorineural hearing impairment, a lower than normal calcium level and normal renal function. Direct sequencing after PCR amplification of genomic DNA revealed a novel insertional mutation (405insC) in the GATA3 gene of both patients. This mutation was hypothesized to disrupt dual zinc fingers as well as one transactivating domain. The present findings lend additional support to the notion that the phenotype cannot be precisely estimated from the genotype in HDR syndrome.