Background The plasma concentration of B‐type natriuretic peptide (BNP) is a strong predictor of adverse cardiovascular events. The aim of this study was to determine whether the association between plasma BNP concentration and cardiovascular mortality is sustained or diminishes with increasing time after BNP is measured. Methods and Results Six thousand seven hundred forty patients with a history of myocardial infarction or unstable angina who participated in the LIPID (Long‐Term Intervention with Pravastatin in Ischemic Disease) trial had plasma BNP concentration measured at baseline and after 1 year. Associations with cardiovascular mortality were evaluated in landmark analyses 1 to <5, 5 to <10, and 10 to 16 years after randomization. There were 1640 cardiovascular deaths. The cardiovascular mortality rate increased progressively from 10.2 to 19.1 to 26.3/1000 patient‐years from 1 to <5, 5 to <10, and 10 to 16 years after baseline, respectively. The average of baseline and 1‐year BNP concentration was more strongly associated with cardiovascular mortality compared with baseline or 1‐year BNP only. The hazard ratio (HR) for cardiovascular death associated with each doubling of average BNP concentration was similar during years 1 to <5 (HR, 1.53 [95% CI, 1.44–1.63]), years 5 to <10 (HR, 1.52 [95% CI, 1.44–1.60]), and years 10–16 (HR, 1.43 [95% CI, 1.36–1.50]), P <0.0001 for all. Conclusions BNP concentration remains an independent predictor of cardiovascular mortality more than a decade after it is measured. Because of random variation in plasma concentrations, the average of >1 BNP measurement improves long‐term risk prediction.