Central hereditary diabetes insipidus is a genetic disorder characterized by polydipsia and polyuria. Most known mutations are located in the arginine-vasopressin (AVP) gene. Here, we describe a Swiss family with an autosomal dominant mutation in the AVP gene region encoding for the carrier protein neurophysin II (P55R). In addition, we discuss the algorithm for diagnosing and treating patients with hereditary central DI based on this Swiss family.