Background: Infective endocarditis is a serious disease with a high mortality even with optimal treatment and care. A number of complicating conditions are known to be of importance for the outcome. But only few data are available in IE patients on the independent prognostic value of kidney function at the time of admittance. Methods: In a prospective observational cohort study data from 235 consecutive IE patients were collected at 2 tertiary heart centres in Copenhagen. Kidney function was evaluated as Estimated Endogenous Creatinine Clearance (EECC) calculated at the time of admission. Patients were divided into 4 groups according to their EECC: 1) > 90 ml/min, 2) 60-90 ml/min, 3) 30-60 ml/min and 4) < 30 ml/min. Mortality statistical analysis was then applied. Results: >Gender: 70.2% male, mean age: 61.3 ± SD 15.0. The most common pathogens were streptococcus species (32.9%) and Staphylococcus aureus (21.8%). Mean follow-up time was 453 days (SD 350). A total number of 76 patients died (32%), with an in-hospital mortality of 14%, and a post discharge mortality of 18%. In 64.9% EECC was decreased at time of admission, and a highly significant relationship between EECC and mortality was demonstrated, P < 0.001. For every decrease of 10 ml/min in EECC we found an increase in Hazard Ratio for mortality of 23.1% (CI 13.2-33.8), P < 0.001. Conclusion: Decreased kidney function is prevalent in patients with endocarditis. Calculated EECC at the time of admission is easily obtained in all IE patients and has a high and independent predictive prognostic value for mortality.