Background: The exponential increase in FDA-approved indications for immune checkpoint inhibitors (ICI) in cancer care has resulted in therapeutic success but also in the occurrence of immune-related adverse effects (irAEs) that can represent a significant clinical challenge. On October 3 2017, the Massachusetts General Hospital (MGH) implemented the Severe Immunotherapy Complications (SIC) Service, a multi-disciplinary care team for patients hospitalized with irAEs. The objectives of this study were to evaluate the impact of SIC Service on 1) healthcare utilization and 2) patients outcomes. Methods: Using pharmacy and hospital admission databases, a list of patients was identified that both received ICI for a malignancy and were hospitalized with severe irAEs in the period prior to initiation of the SIC service and after SIC initiation. The pre-SIC period was defined as an admission between 4/2/2016 through 10/3/2017, and the post-SIC period as an admission from 10/3/2017 through 10/24/2018. The rate of readmission after the index hospitalization was the primary outcome. Secondary outcomes included lengths of stay (LOS) for both initial irAE admissions and readmissions, use of corticosteroids and non-steroidal second-line immunosuppression, ICI discontinuation, and inpatient mortality in the pre- and post-SIC periods. Results: Among 1169 patients treated in the pre-SIC service intervention period; 127 were hospitalized for irAE. Among 1159 patients treated in the post-SIC intervention 122 were hospitalized for irAE. SIC Service implementation was associated with a significant reduction in irAE readmission rates (post-SIC 14.8% vs. pre-SIC 25.9%; odds ratio [OR], 0.46; 95% CI, 0.22-0.95; p=0.036). The length of stay, rates of corticosteroid use, second-line immunosuppression, and ICI discontinuation for irAE, as well as inpatient mortality rates were not significantly different before and after SIC Service implementation. Conclusions: This is the first study to report that establishing a highly subspecialized care team focused on irAEs can be associated with improved clinical outcomes for patients receiving ICI therapy. Such care teams may play an essential part in optimizing irAE care.