BACKGROUND: Pembrolizumab has a manageable safety profile as described in its label, which was primarily based on 2799 patients who participated in clinical trials for melanoma or non-small cell lung cancer. Here, we evaluated the safety of pembrolizumab in a broader population of patients from 31 advanced cancer clinical trials across 19 cancer types. METHODS: Safety was analyzed in patients who received at least one dose of pembrolizumab (200 mg every 3 weeks [Q3W], 10 mg/kg Q2W or Q3W, or 2 mg/kg Q3W). Adverse events (AEs) and immune-mediated AEs and infusion reactions were evaluated. RESULTS: Safety data from 8937 patients in 31 trials of pembrolizumab monotherapy were pooled (median, seven administrations; range, 1-59). Median duration on treatment was 4.1 months (range, 0.03-40.1). AEs occurred in 96.6% of patients. Grade 3-5 AEs occurred in 50.6% of patients. AEs led to pembrolizumab discontinuation in 12.7% of patients and death in 5.9%. Immune-mediated AEs and infusion reactions occurred in 23.7% of patients (4.6% experienced multiple immune-mediated AEs/infusion reactions) and led to pembrolizumab discontinuation in 3.6% and death in 0.2%. Grade 3-5 immune-mediated AEs occurred in 6.3% of patients. Serious immune-mediated AEs and infusion reactions occurred in 6.0% of patients. Median time to immune-mediated AE onset was 85 days (range, 13-163). Of 2657 immune-mediated AEs, 22.3% were initially treated with prednisone ≥ 40 mg/day or equivalent, and 8.3% were initially treated with lower steroid doses. CONCLUSIONS: This pooled analysis of 31 clinical trials showed that pembrolizumab has a consistent safety profile across indications.