Background: Patients with vascular anomalies (VAs) experience poor communication and have unmet information needs. Online patient portals could mitigate communication barriers and support communication interventions. However, these portals are often underutilized. Procedure: We retrospectively queried audit-log data from the Electronic Health Record (EHR) of a single large academic healthcare center for all patients seen by clinicians from a multidisciplinary specialist clinic with a diagnosed VA from 1/2020 to 1/2024. We connected audit-log data with patient demographics to examine how patients used the portal, and whether use varied by patient characteristics. Results: We queried portal usage for 315 patients with vascular anomalies, of whom 43% were children, 19% were adolescents, and 38% were adults. Approximately half of patients’ portals were logged into during the study period (51%, n=162). Of users who ever logged into the portal, the median number of logins per year were 35 (interquartile range 15 to 95). Multiple regression results show that portal access was higher for patients who are White, reside in a metropolitan area, and have lower Area Deprivation Index. Of users who ever logged into the portal, 77% viewed clinician notes, 90% viewed test results, and 71% engaged in messaging with a clinician at least once. Conclusion: Half of patients and caregivers never use the portal, and patients from less urban areas with higher deprivation are even less likely to use the portal. As portals become more integrated into patient care, these inequities in portal access could lead to inequities in health outcomes.