Background: Anemia is common in patients with heart failure (HF) and is associated with worse outcomes. However, the effects of anemia are unknown in an unselected group of HF patients encountered in routine clinical practice in Japan. The impact of anemia on long-term outcomes including mortality and rehospitalization among patients hospitalized with HF was thus assessed. Methods and Results: The Japanese Cardiac Registry of Heart Failure in Cardiology (JCARE-CARD) prospectively studied the characteristics and treatments in a broad sample of patients hospitalized with worsening HF and the outcomes were followed. Study cohorts (n=1,960) were classified into 4 groups by discharge hemoglobin quartiles: <10.1 g/dl (n=482), 10.1-11.9 g/dl (n=479), 12.0-13.6 g/dl (n=487), and ≥13.7 g/dl (n=512). Of the total cohort of HF patients, 57% had anemia, defined by using the World Health Organization definition. Patients with lower hemoglobin quartiles had higher rates of all-cause death, cardiac death, and rehospitalization due to worsening HF. After multivariable adjustment, the risk for all-cause death, cardiac death, and rehospitalization significantly increased with low hemoglobin concentrations. Conclusions: Anemia was quite common especially in patients with HF encountered in routine clinical practice in Japan, and lower hemoglobin was independently associated with long-term adverse outcomes in these patients. (Circ J 2009; 73: 1901-1908)