We have previously identified a single-item measure for baseline overall quality of life (QOL) as a strong prognostic factor for survival, and that fatigue was an important component of patient QOL. To explore whether patient-reported fatigue was supplemental or redundant to the prognostic information of overall QOL, we performed a patient-level pooled analysis of 43 North Central Cancer Treatment Group (NCCTG) and Mayo Clinic Cancer Center (MCCC) oncology clinical trials assessing the effect of baseline fatigue on overall survival (OS). 3,915 patients participating in 43 trials provided data at baseline for fatigue on a single-item 0-100 point scale. OS was tested for association with clinically deficient fatigue (CDF, score 0-50, n = 1,497) versus not clinically deficient fatigue (nCDF, score 51-100, n = 2,418). We explored whether fatigue contributed to overall survival in the presence of performance status and overall QOL. We used Cox proportional hazards models that adjusted for the effects of overall QOL, performance score, race, disease site, age and gender. Baseline fatigue was a strong predictor of OS for the entire patient cohort (CDF vs. nCDF: 31.5 months vs > 83.9 months, p < 0.0001). The effect sizes of fatigue on survival were more variable across different disease sites than was seen for overall QOL (GI, esophageal, head and neck, prostate, lung, breast and others). After controlling for covariates, including performance status and overall QOL, baseline fatigue remained a strong prognostic factor in multivariate models (CDF vs. nCDF: HR = 1.23, p = 0.02). Baseline fatigue is a strong and independent prognostic factor for OS over and above performance status (PS) and overall QOL in a wide variety of oncology patient populations. Single-item measures of overall QOL and fatigue can help to identify vulnerable subpopulations among cancer patients. We recommend these single-item measures for routine inclusion as a stratification factor or key covariate in the design and analysis of oncology treatment trials.