Low molecular weight heparin offers several advantages concerning therapeutic efficacy and safety as compared to unfractionated heparin. Due to renal clearance of low molecular weight heparin problems with the use of low molecular weight heparins may occur in patients with renal failure. Current experience using low molecular weight heparin in patients with renal failure is based on single-dose pharmacokinetic studies, on retrospective analysis and on non-randomized prospective studies. Large randomized studies investigating the use of low molecular weight heparin (e. g. in acute coronary syndrome) have excluded patients with renal failure. Based on the findings mentioned above, treatment with low molecular weight heparin in patients with severe renal failure should follow only under special conditions. In moderate to severe renal failure monitoring anti-Xa activity may be useful to avoid bleeding complications. A definite cut-off level for a potential increase of bleeding complications with the use of low molecular weight heparins in renal failure has not been defined.