Classic Rett syndrome (RS) has been described in females only. Although an X chromosome origin is probable, it has not been substantiated. It is possible, therefore, that RS could occur in males. The authors describe a male with RS and review all the reported cases involving male patients. The authors compare their patient to the other patients and examine the applicability of the classic RS diagnostic criteria to this variant. To date, nine male patients with RS have been reported. The authors describe an additional male who met seven of nine necessary criteria and six of eight supportive criteria as defined by the RS Diagnostic Criteria Work Group. When the authors applied these criteria to the other nine reported patients, many necessary inclusion criteria were not met despite the absence of exclusion criteriThe supportive criteria were even more variable and limited in many patients. In conclusion, males with RS appear to represent a heterogeneous phenotype, with clinical features that may meet many but not all of the necessary diagnostic criteria of classic RS. Less restrictive criteria are needed to include this variant, which should be considered when evaluating males with idiopathic developmental regression, autistic features, and loss of hand function.