Mutations in the coding sequence of the androgen receptor (AR) gene result in a wild range of androgen insensitivity (AI) syndromes. Differences in the clinical expression of the same mutation in unrelated patients have been reported. However, this study reports for the first time strikingly different phenotypes among three patients within the same kindred. Two of the patients had a feminine phenotype, suggesting complete AI, but for some pubic hair. The third subject was male with partial AI, perineoscrotal hypospadias, and cryptorchidism. 5 alpha-reductase activity measured in genital skin fibroblasts and binding capacity of the AR were higher in the male than in the two patients with female phenotype. Northern blot analysis of AR messenger RNA revealed a 10-kb band of normal intensity in the three subjects. Molecular analysis of the coding sequence of the AR revealed a unique M780I mutation in exon 6, changing a methionine 780 to isoleucine in the hormone-binding domain. In conclusion, the same mutation of the AR gene in the same family can result in clinical phenotypes characteristic of complete or partial AI. Therefore, the molecular defect of the AR gene may not alone predict the phenotype in families with AI.