While immune checkpoint inhibitors (ICIs) occasionally cause immune-related adverse events (irAEs) in various organs, the prevalence of irAEs and potential risk factors have not been clarified. We identified irAE predictive factors and examined the relationship between the effect of ICIs and irAEs for patients with malignancies. A total of 533 cases treated with ICIs, including programmed death 1 (PD-1), PD-ligand 1 (PD-L1), and cytotoxic T-lymphocyte antigen 4 (CTLA-4), for various malignancies were included retrospectively. We recorded irAEs from medical records and graded them using the Common Terminology Criteria for Adverse Events version 5. Prevalence and predictive factors associated with immune-related liver injury and the relationship between irAE and treatment response were analyzed. During a median of 10 (1-103) cycles with a median follow-up after several ICI initiations of 384 (21-1715) days, irAEs with all grades and with grade ≥ 3 developed in 144 (27.0%) and 57 (10.7%) cases. Cumulative irAE development rates were 21.9, 33.5, and 43.0% in all grades and 8.8, 14.9, and 20.7% in grade ≥ 3 at 5, 10, and 20 cycles, respectively. Patients who received anti-CTLA4 therapy were more likely to develop irAEs compared to those who received anti-PD-1 or anti-PD-L1 monotherapy. Liver injury was the most common irAE. Multivariate analysis identified the combination of PD-1 and anti-CTL-4 antibodies (hazard ratio HR, 17.04; P < 0.0001) and baseline eosinophil count ≥130/μL (HR, 3.01 for < 130; P = 0.012) as independent risk factors for the incidence of immune-related liver injury with grade ≥ 2. Patients who developed irAEs had a higher disease control rate (P < 0.0001) and an increased overall survival rate compared to those without irAEs (P < 0.0001). Combination therapy with anti-PD-1 and anti-CTL-4 antibodies resulted in higher a frequency of irAEs. Baseline absolute eosinophil count was found to be a predictive factor for immune-related liver injury. Occurrence of irAEs may be associated with higher efficacy of ICI treatment and longer survival among patients who receive ICI therapy.