Background and Methods: We report historical information from longitudinal data held in the British Isles Rett Syndrome Survey (BIRSS) concerning women of at least 40 years. This information, including comments on the quality of care, has been provided by families, carers, and clinicians. Results: Information was available on 30 women with a clinical diagnosis of Rett syndrome (RTT), of whom 24 were < 50 years. Twenty-nine women were diagnosed with classic RTT and one with atypical RTT. Of 18 women tested for "MECP2" mutations, pathogenic variants were identified in 14. There was little increase in severity over time. Conclusions: The study found that: (1) milder phenotypes were common; (2) depression may be under-recognised; (3) menopause does not seem to occur early; (4) nutrition standards from the general population will often be inapplicable; (5) multiple opportunities exist to prevent functional decline through detailed attention to the quality of the medical and social care.