Abstract Background Allogeneic hematopoietic cell transplantation (HCT) is a widely used treatment for hematologic cancers, with survival rates ranging from 25% to 78%. Known risk factors for chronic graft-versus-host disease (cGVHD), a serious and common long-term complication, disease relapse, and mortality following HCT have been identified, but much of the variability in HCT outcomes is unexplained. Biobehavioral symptoms including depression, sleep disruption, and fatigue are some of the most prevalent and distressing for patients; yet research on biobehavioral risk factors for HCT outcomes is limited. This study evaluated patient-reported depression, sleep disruption, and fatigue as risk factors for cGVHD, disease relapse, and mortality. Methods Adults receiving allogeneic HCT for a hematologic malignancy (N = 241) completed self-report measures of depression symptoms, sleep quality, and fatigue (severity, interference) pre-HCT and 100 days post-HCT. Clinical outcomes were monitored for up to 6 years. Results Cox proportional hazard models (2-tailed) adjusting for patient demographic and medical characteristics revealed that high pre-HCT sleep disruption (Pittsburgh Sleep Quality Index >9; hazard ratio [HR] = 2.74, 95% confidence interval [CI] = 1.27 to 5.92) and greater post-HCT fatigue interference (HR = 1.32, 95% CI = 1.05 to 1.66) uniquely predicted increased risk of mortality. Moderate pre-HCT sleep disruption (Pittsburgh Sleep Quality Index 6-9) predicted increased risk of relapse (HR = 1.99, 95% CI = 1.02 to 3.87). Biobehavioral symptoms did not predict cGVHD incidence. Conclusions Biobehavioral symptoms, particularly sleep disruption and fatigue interference, predicted an increased risk for 6-year relapse and mortality after HCT. Because these symptoms are amenable to treatment, they offer specific targets for intervention to improve HCT outcomes.