BACKGROUND: The significance of worsening renal function (WRF) in patients admitted for acute decompensated heart failure (ADHF) is still controversial. We hypothesised that changes in brain natriuretic peptide (BNP) might identify patients with optimal diuretic responsiveness resulting in transient WRF, not negatively affecting the prognosis. Our aim was to verify if in-hospital trends of BNP might be helpful in the stratification of patients with WRF after treatment for ADHF. METHODS: 122 consecutive patients admitted for ADHF were enrolled. Brain natriuretic peptide and eGFR were evaluated at admission and discharge. A 20% relative decrease in eGFR defined WRF, whereas a BNP reduction ≥40% was considered significant. The primary combined endpoint was death/urgent heart transplantation and re-hospitalisation for ADHF. RESULTS: Worsening renal function occurred in 23% of patients without differences in outcome between patients with and without WRF (43% vs. 45%, p=0.597). A significant reduction in BNP levels over the hospitalisation occurred in 59% of the overall population and in 71% of patients with WRF. At a median follow-up of 13.0 (IQR 6-36) months, WRF patients with ≥40% BNP reduction had a lower rate of death/urgent heart transplantation/re-hospitalisation compared to WRF patients without BNP reduction (30% and 75%, respectively; p=0.007). Favourable BNP trend was the strongest variable in predicting the outcome in WRF patients (HR 0.222, 95% CI 0.066-0.753, p=0.016). CONCLUSIONS: Worsening renal function does not affect the prognosis of ADHF and, when associated with a significant BNP reduction, identifies patients with adequate decongestion at discharge and favourable outcome.