Recent case reports of Rett syndrome should help pediatricians recognize this important syndrome. Since the article by Moeschler et al was submitted for publication, new diagnostic criteria for Rett syndrome have been developed and published by a 41-member Rett syndrome Diagnostic Criteria Work Group representing the Centers for Disease Control and the International Rett Syndrome Association. The new diagnostic criteria, which have gained acceptance by investigators worldwide, differ significantly from the older criteria used by Moeschler et al in that they have been separated into necessary, supportive, and exclusion criteria and do not limit Rett syndrome to females.