The fibrosis-4 (FIB-4) index is a non-invasive marker of liver fibrosis. The FIB-4 index predicts poor outcomes in patients with hepatic and non-hepatic diseases. However, the association of the FIB-4 index with mortality and liver-related clinical outcomes following cord blood transplantation (CBT) is unclear. We retrospectively evaluated the impact of the pretransplant FIB-4 index on outcomes in 336 adults following single-unit unrelated CBT at our institution. In multivariate analyses, when the FIB-4 index <1.3 group was used as the reference, non-relapse mortality was significantly higher in the FIB-4 index 1.3-2.67 (hazard ratio [HR], 2.51; 95% confidence interval [CI], 1.19-5.30) and FIB-4 index >2.67 (HR, 2.34; 95% CI, 1.12-4.90) groups. Overall mortality was significantly higher in the FIB-4 index >2.67 group (HR, 1.66; 95% CI, 1.00-2.73), but with only marginal significance in the FIB-4 index 1.3-2.67 group (HR, 1.59; 95% CI, 0.96-2.64). Hematopoietic recovery, acute and chronic graft-versus-host disease of the liver, and veno-occlusive disease/sinusoidal obstruction syndrome were not associated with the pretransplant FIB-4 index. The pretransplant FIB-4 index is accurate and useful in predicting mortality in adult patients undergoing single-unit unrelated CBT.