Percutaneous catheterization of the central venous system is a valuable and commonly employed procedure, but it is not without risk. Two cases are reported which illustrate complications of both internal jugular and subclavian vein cannulation: a fatal cerebrovascular accident; and hemo- and pneumothorax. Literature review indicates that pneumothorax and air embolus are major complications of both routes of catheter insertion. Additionally each route has untoward effects related to the proximity of easily compromised structures (pleura, lungs, arteries, nerves). Awareness of potential complications and use of precautionary measures may reduce the risk of these procedures.