Background: Hepatic adverse events (AEs) are commonly encountered during ICI treatment in cancer. We evaluated the incidence and impact of hepatic AEs in a territory-wide cohort of 1509 patients who received ICI for cancer treatment. Methods: This is a territory-wide retrospective observational cohort study in Hong Kong. We identified patients through the regional hospital database (CDARS), based on the drug record of ICIs from 1 Jan 2014 to 31 Oct 2018. Serial liver functions before, during and at 3-month after ICI, were retrieved. Hepatic AEs were graded according to CTCAE 4.0. Results: The mean age was 60 years and 65.4% were male with the commonest malignancies being lung cancer (37.0%), liver cancer (17.0%) and gastrointestinal (GI) cancer (8.4%). Grade 1-2 and grade 3-4 hepatic AE occurred 39.8% and 23.3% of patients, respectively, during or within 3 months after ICI. During ICI, 39.5% developed grade 1-2 and 13.0% had grade 3-4 hepatic AE. The most common manifestations of hepatic AE occurred as elevation of ALT/AST (grade 1-2: 38.7%; grade 3-4: 10.3%). The median time of duration from ICI 1^st dose to hepatic ≥ Grade 3 AE was 54 days (IQR: 22-124). Patients with liver cancer were more likely to develop hepatic AE (grade 1-2: 37.4%; grade 3-4: 55.5%). In all patients and cancer subgroup, patients with grade 3-4 hepatic AE had worse OS than grade 1-2 hepatic AE (Table). Conclusions: Hepatic AE occurs in more than half of the patients receiving ICI, with over 20% being grade 3-4 AE. Regardless of tumor types, development of hepatic AE during ICI is associated with poor prognosis.