We examined whether male pseudohermaphroditism, when unexplained, is associated with reduced prenatal growth. Birth weight SD scores of 29 children with male pseudohermaphroditism were compared. The scores of children with an unexplained condition (median -2.1 SD) were found to be lower (p = 0.0001) than those of children with an explained condition (median -0.4 SD). In the majority of cases of unexplained male pseudohermaphroditism, there was a complicated history before conception or in early pregnancy. In conclusion, hitherto unexplained male pseudohermaphroditism was found to be associated with reduced prenatal growth and complications at conception or in early pregnancy.