Background. It has been suggested that low thyroid hormones levels may be associated with increased mortality in patients with cardiovascular disease. Aim. To evaluate the prognostic role of thyroid function deficiency in patients with chronic heart failure (CHF). Methods. We evaluated 338 consecutive outpatients with stable CHF receiving conventional therapy, all of whom underwent a physical examination, electrocardiography and echocardiography. Blood samples were drawn to assess renal function, and Na+, hemoglobin, NT-proBNPs, fT3, fT4 and TSH levels. Patients with hyperthyroidism were excluded. Results. During the follow-up (15±8 months), heart failure progression was observed in 79 patients (including 18 who died of heart failure after hospitalisation and six who underwent transplantation). Univariate regression analysis showed that TSH (p < 0.0001), fT3 (p < 0.0001), fT4 (p=0.016) and fT3/fT4 (p < 0.0001) were associated with heart failure progression but multivariate analysis showed that only TSH considered as a continuous variable (p = 0.001) as well as subclinical hypothyroidism (TSH mUI/l; p=0.014) remained significantly associated with the events. Conclusions. In CHF patients TSH levels even slightly above normal range are independently associated with a greater likelihood of heart failure progression. This supports the need for prospective studies aimed at clarifying the most appropriate therapeutic approach to sub-clinical hypothyroidism in such patients.