Abstract
Polydipsia and polyuria are common symptoms in patients with diabetes insipidus (DI), which can be due to inadequate vasopressin production (cranial DI) or vasopressin insensitivity (nephrogenic DI). Clinical diagnosis of the subtypes of DI can be tricky. We present a 44-year-old man with a strong family history of DI who had been diagnosed with autosomal dominant nephrogenic DI from infancy. At the age of 40, he had progressed to end-stage renal failure. When he experienced unresolving severe polyuria after renal transplant, further investigations revealed that he was misdiagnosed and that he had a novel mutation causing autosomal dominant cranial DI.