A survey of 297 institutionalized adults with mental retardation to determine the prevalence of symptoms of Rett syndrome is reported from the Medical Center Rehabilitation Hospital, Grand Forks, ND and University of North Dakota School of Medicine. The survey suggests that a) male and female adults as a group express the individual symptoms of Rett syndrome with equal frequency, b) as individuals, only females appear to exhibit the full criteria for Rett syndrome, c) males do exhibit particular symptoms of the syndrome, and d) no individual symptom or two symptoms separate males and females. The prevalence rate for Rett syndrome in the institutionalized population of persons with mental retardation was 1:46 for females and 1:116 for both sexes. Midline hand stereotypies, hyperventilation, impaired ambulation, seizures, and absence of prenatal complications all occurred with equal frequency in both sexes. 
COMMENT. The oldest of the four females who met the strict and necessary criteria for the diagnosis of Rett syndrome was 40 years of age. The female sex is no longer considered a necessary diagnostic criterion and a less restrictive symptom complex is proposed by some authorities.