Cancer patients have additive risk factors for thrombosis especially if permanent central catheters (port systems) are used for the delivery of chemotherapy. In our hospital the rate of thrombotic complications is below 5% for cancer patients receiving chemotherapy via port systems. This is in contrast to clinical studies, which have shown that up to 60% of catheters acquire clots that obstruct more than 50% of the vascular lumen. It is reasonable to believe that complications arising from thrombotic catheter alterations, such as bacterial hosting or micro-emboli, are clinically underestimated. The identification of thrombotic alterations of permanent central venous catheters in cancer patients receiving chemotherapy is substantial for the estimation whether anticoagulation strategies should be used as prophylaxis.