Though children with Perlman and Wiedemann-Beckwith syndromes have a number of features in common, the two conditions are probably separate entities. The distinction may not always be easy, however, partly because of the extreme rarity of Perlman syndrome, only nine cases of which have been reported so far. We report two siblings, initially diagnosed as having Wiedemann-Beckwith syndrome, in whom the correct diagnosis of Perlman syndrome was made only after an autopsy on the second child. By comparing and contrasting the features of Perlman and Wiedemann-Beckwith syndromes in this report we hope to make it easier to distinguish the two conditions.