Hypospadias is a common urological abnormality and may occur in simple (glandular or penile) or severe forms (perineal). Perineal hypospadias often occurs in association with other genital abnormalities, such as bilateral cryptorchidism and micropenis, and may be the result of partial androgen insensitivity. We have investigated the androgen binding status and androgen receptor gene of boys from two unrelated families. The first pair of brothers had partial androgen insensitivity with perineal hypospadias, bilateral cryptorchidism, and micropenis, while the other boys had isolated perineal hypospadias. Qualitative androgen binding defects were shown in both sets of brothers and different point mutations of the androgen receptor gene were found in the two families. These findings suggest that the genital abnormalities in the affected brothers result from defects in the androgen receptor. Furthermore, severe familial hypospadias may be a previously unrecognised part of the phenotypic spectrum of the partial androgen insensitivity syndrome. This study provides valuable information for the genetic counselling of families affected by this X linked genital abnormality.