PURPOSE: Nonsteroidal anti-inflammatory drugs (NSAIDs) may be associated with severe renal complications, including acute renal failure, reduced glomerular filtration rate and interstitial nephritis. Caution against NSAIDs is therefore recommended in advanced chronic kidney disease. In this study, we examined NSAID use, aetiology and comorbidity among a national cohort of patients before the initiation of chronic renal replacement therapy (RRT). METHODS: Patients initiated on chronic RRT in the period 1997-2006 were identified in the Danish National Registry on Regular Dialysis and Transplantation, including etiological diagnosis. The use of NSAID before the start of RRT was studied by linkage to the National Prescription Register and comorbidity by linkage to the National Patient Registry. RESULTS: A total of 6663 patients were included in the study, and 2407 patients (36.1%) were prescribed NSAID in the 3¿years before the start of RRT. These patients were older (mean age = 63.0 vs 61.4¿years) and had a significantly higher degree of comorbidity (Charlson score = 2.85 vs 2.61, p¿