BACKGROUND: Transcranial Doppler (TCD) can be used in the diagnosis and monitoring of reversible cerebral vasoconstriction syndrome (RCVS). Whether TCD abnormalities can extend beyond 8-12 weeks has not been studied. We performed a single-center, retrospective analysis of TCD abnormalities in RCVS, specifically, whether elevated mean flow velocities (MFV) can persist beyond 90 days of symptom onset. METHODS: Consecutive patients were identified retrospectively using our hospital coding and billing data, and EMR search (2012-2023). Inclusion criteria were diagnosis ofRCVS, any age, and available Spectral TCD (non-imaging) (TCD-S). Exclusion criteria were RCVS patients without TCD-S studies, or patients deemed to have other vasculopathies upon adjudication. We recorded demographics, RCVS triggers, and clinical and imaging features. Presence of elevated MFV on TCD-S above the upper reference range was considered abnormal. RESULTS: Ninety patients with RCVS had TCD-S performed (mean age 39.8 ± 11.8 years, 91% female). Six patients (6.7%) were pregnant and 25 (27.8%) were postpartum. Vasoconstriction was seen on imaging in 56 (62.2%). Median RCVS CONCLUSIONS: Patients with RCVS can have elevated TCD-S mean flow velocities beyond 90 days. TCD-S may have utility in the diagnosis of RCVS in the early or mild cases, where CTA or MRA may not capture the vasospasm. Prospective studies of the duration of TCD-S abnormalities are necessary to confirm these findings, and to inform clinical management, such as the duration of follow-up and the effects of calcium channel blocker treatment.