Intensive care unit patients have multiple risk factors for venous thromboembolism. Venous thromboembolism leads to significant morbidity and can be fatal. Unfractionated heparin and low molecular weight heparin are commonly used to prevent venous thromboembolism. Heparin induced thrombocytopenia, an untoward consequence of exposure to heparin, is an immune disorder that may develop in patients treated with heparin products. Determining the prevalence of heparin induced thrombocytopenia and its relationship to preventive and therapeutic heparin and low molecular weight heparin will help clinicians more appropriately choose methods of venous thromboembolism prophylaxis and treatment in the critically ill, ICU population.