Background Iron deficiency (ID) is an emerging problem in patients with chronic heart failure (HF) and can be a potential therapeutic target. However, not much is known about the prevalence, predictors, and prognosis of ID in patients with chronic HF. Methods In an international pooled cohort comprising 1,506 patients with chronic HF, we studied the clinical associates of ID and its prognostic consequences. Results Iron deficiency (defined as a ferritin level <100 μg/L or ferritin 100-299 μg/L with a transferrin saturation <20%) was present in 753 patients (50%). Anemic patients were more often iron deficient than nonanemic patients (61.2% vs 45.6%, P < .001). Other independent predictors of ID were higher New York Heart Association class, higher N-terminal pro-brain-type natriuretic peptide levels, lower mean corpuscular volume levels, and female sex (all P < .05). During follow-up (median 1.92 years, interquartile range 1.18-3.26 years), 440 patients died (29.2%). Kaplan-Meier survival analysis revealed ID as a strong predictor for mortality (log rank χ2 10.2, P = .001). In multivariable hazard models, ID (but not anemia) remained a strong and independent predictor of mortality (hazard ratio 1.42, 95% confidence interval 1.14-1.77, P = .002). Finally, the presence of ID significantly enhanced risk classification and integrated discrimination improvement when added to a prediction model with established risk factors. Conclusions Iron deficiency is common in patients with chronic HF, relates to disease severity, and is a strong and independent predictor of outcome. In this study, ID appears to have greater predictive power than anemia.