BACKGROUND & AIMS: Metabolic dysfunction-associated steatohepatitis (MASH) and fibrotic MASH are significant health challenges. This multi-national study aimed to validate the acMASH index (including serum creatinine and aspartate aminotransferase concentrations) for MASH diagnosis and develop a new index (acFibroMASH) for non-invasively identifying fibrotic MASH and exploring its predictive value for liver-related events (LREs). METHODS: We analyzed data from 3004 individuals with biopsy-proven metabolic dysfunction-associated steatotic liver disease (MASLD) across 29 Chinese and 9 international cohorts to validate the acMASH index and develop the acFibroMASH index. Additionally, we utilized the independent external data from a multi-national cohort of 9034 patients with MASLD to examine associations between the acFibroMASH index and the risk of LREs. RESULTS: In the pooled global cohort, the acMASH index identified MASH with an area under the receiver operating characteristic curve (AUROC) of 0.802 (95% confidence interval [CI], 0.786-0.818). The acFibroMASH index (including the acMASH index plus liver stiffness measurement) accurately identified fibrotic MASH with an AUROC of 0.808 in the derivation cohort and 0.800 in the validation cohort. Notably, the AUROC for the acFibroMASH index was 0.835 (95% CI, 0.786-0.882), superior to that of the FAST score at 0.750 (95% CI, 0.693-0.800; P < .01) in predicting the 5-year risk of LREs. Patients with acFibroMASH >0.39 had a higher risk of LREs than those with acFibroMASH <0.15 (adjusted hazard ratio, 11.23; 95% CI, 3.98-31.66). CONCLUSIONS: This multi-ethnic study validates the acMASH index as a reliable, noninvasive test for identifying MASH. The newly proposed acFibroMASH index is a reliable test for identifying fibrotic MASH and predicting the risk of LREs.