Objectives: Liver fibrosis is independently associated with pulmonary arterial hypertension (PAH). Investigating the relationship between liver fibrosis and PAH may provide mechanistic insight into this relationship. In this study, we aimed to elucidate the relationship between the fibrosis-4 (Fib-4) index and PAH. Materials and Methods: In this retrospective, single-center cohort study, 61 patients diagnosed with PAH were included. During a median follow-up period of 27 months, Fib-4 indexes calculated from alanine aminotransferase, partate aminotransferase, and platelet values at the time of PAH diagnosis were evaluated in patients who experienced mortality and survived. Results: During the subsequent evaluation of the study cohort, 20 patients were found to have experienced mortality. The group with mortality had higher Fib-4 scores (1.6±0.22 vs. 0.69±0.4, p=0.003). Independent predictors of mortality and the diagnostic performance of the Fib-4 index were analyzed by ROC curve analysis. Accordingly, the predictive value of the Fib-4 index for mortality was >1.02, with a sensitivity of 77% and specificity of 72% (area under the curve: 0.824, 95% confidence interval: 0.740-0.880). Conclusion: The Fib-4 index, a straightforward and valuable metric, can be used as a prognostic marker for mortality in patients with PAH.