Outside of clinical trials and before commercial availability for acute and chronic graft-versus-host disease (GVHD), the Janus kinase (JAK) 1/JAK2 inhibitor ruxolitinib was available to US patients with steroid-refractory GVHD through an open-label, multicenter expanded access program (EAP) sponsored by Incyte Corporation. To assess the safety of ruxolitinib, data on serious adverse events (SAEs) reported among patients in the EAP were collected. Patients ≥12 years old who received allogeneic hematopoietic cell transplantation for a hematologic malignancy and developed any-grade acute or chronic steroid-refractory GVHD received ruxolitinib at a starting dose of 5 mg twice daily (BID; acute GVHD) or 10 mg BID (chronic GVHD). At data extraction (May 8, 2020), 60 patients with acute GVHD and 549 with chronic GVHD were enrolled. In the acute and chronic GVHD cohorts, 41 (68.3%) and 186 (33.9%) patients, respectively, had ≥1 SAE. Sepsis (8.3%) and respiratory failure (6.7%) were the most common SAEs in the acute GVHD cohort, and pneumonia (4.9%), sepsis (3.8%), and lung infection (3.5%) in chronic GVHD. Infection SAEs were reported in 23.3% and 20.0% of patients with acute and chronic GVHD, respectively. Overall, these safety findings demonstrate the tolerability of ruxolitinib in steroid-refractory GVHD.