Brain natriuretic peptide (BNP) is a marker of systolic and diastolic dysfunction and a strong predictor of mortality in heart failure patients. The present study aimed to assess the relationship of BNP with aortic stenosis (AS) severity and prognosis. The cohort comprised 289 high-risk patients with severe AS who were referred for transcatheter aortic valve implantation. Patients were divided into tertiles based on BNP level: I (n = 96); II (n = 95), and III (n = 98). Group III patients were more symptomatic, had higher Society of Thoracic Surgeons and EuroSCORE scores, and had a greater prevalence of renal failure, atrial fibrillation, and previous myocardial infarction; lower ejection fraction and cardiac output; and higher pulmonary pressure and left ventricular end diastolic pressure. The degree of AS did not differ among the 3 groups. Stepwise forward multiple regression analysis identifies ejection fraction and pulmonary artery systolic pressure as independent correlates with plasma BNP. Mortality rates during a median follow-up of 319 days (range 110 to 655) were significantly lower in Group I compared with Groups II and III, p <0.001. After multivariable adjustment, the strongest correlates for mortality were renal failure (hazard ratio 1.44, p = 0.05) and medical/balloon aortic valvuloplasty (HR 2.2, p <0.001). Mean BNP decreased immediately after balloon aortic valvuloplasty from 1,595 ± 1,229 to 1,252 ± 1,076, p = 0.001 yet increased to 1,609 ± 1,264, p = 0.9 at 1 to 12 months. After surgical aortic valve replacement, there was a nonsignificant, immediate decrease in BNP level from 928 ± 1,221 to 896 ± 1,217, p = 0.77, continuing up to 12 months 533 ± 213, p = 0.08. After transcatheter aortic valve implantation, there was no significant decrease in BNP immediately after the procedure; however, at 1-year follow-up, the mean BNP level decreased significantly from 568 ± 582 to 301 ± 266 pg/dl, p = 0.03. In conclusion, a high BNP level in high-risk patients with severe AS is not an independent marker for higher mortality. BNP level does not appear to be significantly associated with the degree of AS severity but does reflect heart failure status.