We examined the nucleotide sequence of the arginine vasopressin-neurophysin II gene in three kindreds with autosomal dominant neurohypophyseal diabetes insipidus. Each of the three different mutations identified represents a recurrence of a mutation previously described to cause this disease. These mutations are all transitions (C1761-->T, G1859-->A, and G279-->A) that encode amino acid substitutions Pro24-->Leu, Gly57-->Ser (both in neurophysin II), and Ala-->Thr (in the last amino acid at the C-terminus of the signal peptide). The presence of these mutations in genomic DNA was confirmed by alterations in restriction endonuclease recognition sites. A linkage map of distal chromosome 20 was constructed. To examine the possibility that these apparent recurrent mutations arose independently rather than by an ancestral founder mutation, we analyzed family origins, two polymorphic markers on chromosome 20 in close proximity with this gene (the oxytocin/XbaI restriction fragment length polymorphism and the D20S57 polymorphic CA repeat microsatellite), and/or the occurrence of a de novo mutation in our three families and in four additional families previously reported. Our results suggest that one of our families may share an ancestral founder mutation with one previously reported family, but that in the remainder of the families with identical mutations, these mutations probably arose independently.