Background: Whether COVID-19 vaccination and the associated immune response increases susceptibility to immune-related adverse events (irAEs) among patients treated with immune checkpoint inhibition (ICI) remains unknown. Short-term follow-up can assess the safety of concurrent administration of the vaccine and ICI treatment. Methods: We conducted an electronic health record analysis of a cohort of 408 patients with cancer receiving ICI therapy and who were vaccinated for COVID-19 between January 16 and March 27, 2021. Patients were seen in follow-up for 90 days from the day of the first dose in this single-institution tertiary care center. We evaluated the incidence of irAEs and the frequency of each event type and grade among patients who experienced an irAE. We also evaluated the incidence of irAEs in patients who began a new immunotherapy agent after vaccination. Results: Among 408 patients with cancer receiving ICI therapy (median age, 71 years; 217 [53%] male), administration of a COVID-19 mRNA vaccine within 90 days of ICI treatment was not associated with an increased incidence of irAEs. A total of 27 (7%) patients experienced a new irAE within the observation period. Among patients with previous irAEs from ICIs (n=54), 3 (6%) experienced a recurrent irAE, and of those initiating a new immunotherapy (n=52), 9 (17%) experienced an irAE. No excess risk of COVID-19 diagnosis was seen in this subset of patients receiving ICI therapy, and no breakthrough COVID-19 cases were seen after full COVID-19 vaccination. Conclusions: These findings should reassure providers that COVID-19 vaccination during ICI therapy is safe and efficacious.