The incidence of neurological deficits of the upper extremity was studied in a prospective trial on 201 consecutive patients who underwent median sternotomy at cardiac surgery. In 13 patients (6.5%), a brachial plexus paresis was diagnosed postoperatively. We were unable to demonstrate any statistically significant correlation between brachial plexus paresis and the side of arm placement, the side of cannulation of the jugular vein, the duration of operation, the bypass time, sex, or type of operation. All patients who suffered from neurological deficit were aged 50 years and more, however without any statistically significant correlation. In our opinion, brachial plexus lesions following median sternotomy in cardiac surgery depend on the extent of sternal spread and the height of placement of the retractor in dependence of the rigidity of the rib cage. By reason of the iatrogenic cause of brachial plexus lesions, it appears to us that these complications should be included in those of which the patient needs to be informed preoperatively.