One hundred twelve consecutive patients with acute ascending aortic dissection and submitted to immediate surgery were retrospectively analyzed with regard to perioperative mortality and morbidity. The patients were divided into two groups according to whether distal aortic repair was carried out by the open procedure (using deep hypothermic circulatory arrest, group A: 68 patients) or by the closed technique (without circulatory arrest, group B: 44 patients). Patients' ages ranged from 24 to 78 years (mean 57.4 years). No significant difference was found between the two groups in terms of age and sex distribution. However, the prevalence in the extent of clinical and anatomical alterations was significantly higher in group A (hemodynamic instability, pericardial tamponade and neurological deficit). The duration of hypothermic circulatory arrest for group A patients averaged 25 min and ranged from 12 to 65 min. The overall perioperative mortality was 17% (19/112 patients); it was 20.6% (14/68) in group A and 11.4% (5/44) in group B; the difference was not statistically significant but consistent with a clear trend. The trend towards a higher mortality in group A mainly reflected the more severe and complex anatomical characteristics and could not be attributed to the circulatory arrest per se. The period of deep hypothermic circulatory arrest in the survivors (25 min) was similar to that of the group with lethal outcome (32 min). Among the non-lethal complications, however, group A patients more frequently showed clinical signs consistent with cerebral injury: apart from the transient symptoms suggestive in reversible diffuse cerebral damage, five patients in group A had a permanent focal neurological deficit (versus one patient in group B).(ABSTRACT TRUNCATED AT 250 WORDS)