Inferior vena cava (IVC) diameter can be used to approximate right atrial pressure in patients admitted for acute decompensated heart failure (ADHF). Recent studies linked IVC dilation to an increased risk of early re-admission and short-term mortality. Moreover, renal insufficiency (RI) is an established risk factor for mortality in ADHF and is associated with congestion. We hypothesized that the IVC diameter is a marker of all-cause mortality but its prognostic impact may be influenced by kidney function. We analyzed data of 1101 patients admitted for ADHF with available echocardiography of the IVC by chart review and death registry linkage. Patients were dichotomized according to a cut-off value of 21 mm. Cox proportional hazards model was used to identify mortality predictors. A dilated IVC was detected in 474 (43.1%) patients. Overall, 400 (36.3%) patients died within 3 years. All-cause mortality was significantly higher in patients with dilated IVC [hazard ratio 1.45 (confidence interval 1.21–1.74); p < 0.001]. However, a dilated IVC was only associated with all-cause mortality in patients with RI function [hazard ratio 1.60 (confidence interval 1.26–2.03); p < 0.001] but not in patients with a preserved kidney function [hazard ratio 1.04 (confidence interval 0.72–1.50); P = 0.84]. IVC diameter was identified as an independent predictor for all-cause mortality in a Cox proportional hazards model with a significant interaction between IVC diameter and baseline kidney function. In conclusion, IVC dilation is a marker of high mortality risk in patients admitted for ADHF. However, this observation was confined to patients with RI.