Transient neurologic dysfunction (TND) namely postoperative confusion, delirium, and agitation after aortic operation, particularly after deep hypothermic circulatory arrest (DHCA), remains an underestimated adverse event in the early outcome of these patients. Although no influence on long-term outcome has been reported so far, this entity markedly affects the early outcome and leads to prolonged intensive care unit and hospital stay. Between January 1997 and January 2003, 160 consecutive patients (130 type A dissections 81% and 30 elective atherosclerotic aneurysms 19%) had surgical repair with DHCA for a thoracic aortic aneurysm limited to the ascending aorta. From those, 40 patients (25%) underwent DHCA alone, whereas in 13 patients (8%) antegrade cerebral perfusion and in 103 patients (64%) retrograde cerebral perfusion was used for further brain protection. The overall incidence of TND was 18% (28 of 160) with a significant association between duration of circulatory arrest and the incidence of TND (13.8% in DHCA < 30 minutes versus 37.9% in DHCA > 40 minutes; p < 0.05). Furthermore the severity of TND was directly associated with the duration of circulatory arrest and age. In contrast, however, the use of retrograde cerebral perfusion had no influence on the incidence of TND, ( p < 0.05). Intensive care unit stay as well as hospital stay were prolonged in the patients with TND (intensive care unit 14.3 ± 14.2 days versus 10.8 ± 13.7 days, p < 0.05; hospital stay 15.6 ± 10.1 days versus 11.4 ± 7.9 days, p < 0.05). Duration of DHCA, regardless of whether retrograde cerebral perfusion was used, was the most important predictor of the incidence of transient neurologic dysfunction in patients who had replacement of the ascending thoracic aorta. The occurrence of TND leads to impaired functional recovery as well as prolonged intensive care unit and hospital stay.