Hypoparathyroidism with sensorineural deafness and renal dysplasia (HDR) syndrome is an autosomal dominant condition caused by mutations of the gene encoding the dual zinc-finger transcription factor, GATA3. A previous study identified some patients with GATA3 gene variants and breast cancer, suggesting that GATA3 variants may contribute to tumorigenesis in estrogen receptor 1-positive breast tumors; however, these patients did not have HDR syndrome. A 32-year-old nonsmoking Japanese woman was histologically diagnosed with lung squamous cell carcinoma associated with HDR syndrome and a c.C952T>C (p.C318R) germline mutation in GATA3. This is the first report describing cancer in a patient with HDR syndrome. Our data indicates that GATA3 mutations may be a potential therapeutic target for lung cancer.