Diabetic autonomic neuropathy (AN) as a risk factor of surgical procedures has so far been described in case reports, but no controlled clinical studies are known. Therefore, we intended to study systematically the perioperative relevance of the autonomic dysfunction. 32 ophthalmosurgical patients (20 diabetics, 12 non-diabetics) were investigated. Cardiovascular autonomic function was examined preoperatively by a combination of tests (heart rate variations during deep breathing, Valsalva ratio, 30:15 ratio, postural hypotension, sustained hand grip). A scoring system based on these tests provided the staging of the autonomic involvement of the patients (AN score). The anaesthesiological management (thiopentone, N2O, halothane) and the operative procedure (vitrectomy) were uniform. A significant correlation was found between the AN score and the coefficient of variation of the systolic (r = 0.70, p less than 0.001) resp. the diastolic (r = 0.52, p less than 0.01) blood pressure during anaesthesia. No correlation was found between the intraoperative variability of the arterial blood pressure (coefficient of variation) and the age of the patients resp. the preoperative value of the blood pressure. In diabetics with severe autonomic neuropathy (AN score greater than 5) hypotensive reactions were seen very often during the operation. The results demonstrate that the haemodynamic stability in the perioperative period depends on the severity of the autonomic dysfunction. Diabetics with severe autonomic neuropathy have a high risk of blood pressure instability. Non-invasive diagnostic methods allow to identify these patients preoperatively.