Background: Rett Syndrome (RTT) is an X-linked neurodevelopmental disorder, characterized by gradual loss of motor, verbal and social skills. This study describes the epidemiology and healthcare resource utilization (HCRU) of RTT in Ontario, Canada. Methods: RTT patients (≥ one ICD-10-CA code F84.2) were identified using data held at the Institute for Clinical Evaluative Sciences (ICES), between September 2018-August 2023. Incidence and prevalence rates from Ontario were extrapolated nationally using the Stats Can population estimates. Results: A total of 246 patients were indexed; 95% female, median age 21 years and 40% from central Ontario. There were 57 incident and 257 prevalent RTT cases identified in Ontario. National extrapolations estimated 175 incident and 613 prevalent RTT cases. Common comorbidities included developmental disability (85.4%) and epilepsy (49.6%). Patients frequently had outpatient visits (primary care 96.7%, specialists 86.6%), emergency department visits (76.8%) and inpatient hospitalizations (54.5%). Most patients (95.1%) had at least one public claim for all-cause medication. Disease-specific medication claims were for anti-infectives (69.1%) and anti-seizure medications associated with mood effects (65.0%). Conclusions: This study provides population-based estimates of RTT in Canada. Findings highlight the high burden of illness and HCRU of RTT and the opportunities to improve healthcare outcomes in this population.