OBJECTIVE In individuals without cardiovascular disease, elevated body mass index (BMI) is associated with an increased risk of death. However, in patients with certain chronic diseases, including heart failure, low BMI has been associated with increased mortality. We investigated the association between BMI and prognosis in patients with systolic HF. METHODS Follow-up was made on 540 patients (mean age 58.53 years, 84.2% men) with systolic HF (LVEF < or = 45%) and association between BMI and adverse cardiac events was analyzed. RESULTS During a median follow-up of 24 months, 92 patients died including 87 cases of cardiac death and 92 patients were rehospitalized. Compared with patients with BMI higher than 28.0 kg/m(2), patients in lower BMI categories (BMI < or = 18.5 kg/m(2) and > or = 18.5 kg/m(2) < 24.0 kg/m(2)) had a graded increase in the all cause death rate [5.44 (1.78 - 16.66), 4.30 (1.71 - 10.82)], cardiac death rate [OR(95%CI): 5.42 (1.77 - 16.59), 4.00 (1.59 - 10.10)], HF death rate [8.94 (2.37 - 33.74), 4.97 (1.52 - 16.20)] and MACE rate [2.10 (1.09 - 4.07), 1.79 (1.14 - 2.82)]. After adjustment for age, gender, LVEF and NYHA grade using cox regression analysis, BMI categories still significantly associated with all cause death rate (OR = 0.77, P < 0.05), cardiac death rate (OR = 0.78, P < 0.05) and HF death rate (OR = 0.79, P < 0.05). CONCLUSIONS In patients with systolic heart failure, lower BMI was an independent predictor of increased all cause death rate, cardiac death rate and HF death rate.