Abstract Background Elderly patients have the highest prevalence of heart failure (HF). The aims of the study were to establish a reference interval for B-type natriuretic peptide (BNP) and (Nt-proBNP) in elderly people, and to identify clinically relevant decision limits based on long-term outcome. Methods Plasma concentrations of BNP and Nt-proBNP were measured from two elderly populations: 218 healthy subjects (mean age 73 years, population I), and 474 patients (mean age 73 years, population II) with symptoms associated with HF. Study population II was followed for 6 years with registration of all cardiovascular mortality. Results An association between both BNP and Nt-proBNP concentrations and age was found. The upper limit for the reference intervals in the healthy elderly (population I) was: BNP ≤ 28 pmol/L (≤ 97 ng/L), and Nt-proBNP ≤ 64 pmol/L (≤ 540 ng/L). Based on cardiovascular mortality, decision limits for BNP (∼ 50 pmol/L, ∼ 170 ng/L) and Nt-proBNP (∼ 200 pmol/L, ∼ 1700 ng/L) (population II) were determined. Conclusions Besides establishing reference intervals for BNP and Nt-proBNP in an elderly population, a higher clinically relevant decision limit for BNP and Nt-proBNP was identified, indicating additive prognostic information of the peptides on top of measurements by echocardiography. Therefore, both reference intervals and decision limits should be included in clinical practice.