Catheters for large vessels have become essential tools for the management of hospitalized or chronically ill patients requiring intensive medical treatments such as extracorporeal detoxification procedures. The increased use of such devices has been accompanied by a corresponding increase in complications, such as infection, sepsis, and thrombosis. In two retrospective studies, the first (1979-1990) with 1672 patients and 2626 large-bore catheters and the second (1996-2001) with 182 patients and 332 acute catheters, the frequency of infections, thrombosis, bleeding, and other side-effects were investigated. All complications and side-effects are presented. In total, the complication rate was in the first study 27.7% (internal jugular vein 23.8% in 2105 catheters, subclavian vein 43.5% in 521 catheters) and in the second study 32.2% (internal jugular vein 20% in 231 catheters, subclavian vein 60.6% in 94 catheters, femoral vein 57.1% in 7 catheters). The majority of complications were puncture not possible, puncture of the artery abscess, septicemia, bleeding, thrombosis, and faults in catheter material. To minimize these complication rates the handling of the inserted catheters before, during, and after the hemodialysis or apheresis treatment is minimized.