Infections and thromboses are the most frequent complications of central venous catheters (cvc). The use of a special material (i. e. polyurethane, silicone) and type (i. e. Hickman) small in diameter, the avoidance of any infection as well as the optimal position of the cvc tip in the lower part of the vena cava superior and a short period of catheterisation will be effective in decreasing the number of thromboses, whereas other thrombogenic factors (i. e. malignant disease), the patient's age, additional chemo- and/ or radiotherapy cannot practically be influenced. Coated cvc, oral anticoagulants, acetylsalicylic acid, and low dose urokinase, unfractionated and predominantly low molecular weight heparins (LMWH) are in use to avoid thromboses. Our outpatients with progressed gastrointestinal malignancies, port systems, and systemic chemotherapy consequently receive a prophylaxis with LMWH for at least 90 days according to the beneficial results published in three studies. Additional antitumoral effects of LMWH are presently evaluated and will favour consequent LMWH prophylaxis in patients with advanced malignancies and permanent catheters.