Central venous catheterization is utilized in resuscitation and evaluation of the severely ill patient. It is also employed for total parenteral nutrition. The list of potential complications is extensive and includes catheter malposition, with its attendant morbidity, as the most frequent complication. Inaccurate venous pressure measurements and mediastinal phlebitis have been cited as natural sequelae of inadvertent catheterization of the internal thoracic (mammary) vein (ITV). The histories of four patients who had ITV cannulation are analyzed as to indications for central venous catheterizations, site of insertion, time of delayed recognition, and attendant complications. In addition, the records of 150 consecutive patients who underwent central venous line placement were reviewed to determine the number of lines placed (242), the number and percentage of postcatheterization chest films obtained with standard posterior-anterior (P-A) and lateral technique (70, 29%), the number and incidence of catheterization-associated complications (78, 32%), and the number and incidence of ITV cannulation (5, 2%). No untoward results were seen as a result of this complication in the nine patients discovered, although the potential for morbidity was present. Subtle changes on portable chest films and standard technique P-A and lateral films remain the best protection against complications associated with ITV cannulation.