Low-molecular-weight heparin (LMWH) has largely replaced unfractionated heparin for the treatment of venous thromboembolism. The predictable anticoagulant effect of LMWH is seen across almost all patient populations, with few exceptions. However, because LMWH is primarily eliminated through the kidneys, patients with renal insufficiency are at risk of LMWH accumulation and bleeding complications. The risk of LMWH accumulation and bleeding is dependent on several factors including the degree of renal insufficiency, dose and type of LMWH. These risks are greatest when therapeutic doses of LMWH are used in patients with creatinine clearance less than 30 ml/min. Prophylactic dose LMWH does not appear to be associated with an increased bleeding risk, but has not been evaluated in large trials. LMWHs with a higher molecular weight may be less prone to accumulation and bleeding. LMWH must be used carefully in patients with renal insufficiency, particularly in those with severe renal impairment.