A noninvasive follow-up using duplex ultrasonography was conducted in 128 patients who had undergone carotid endarterectomy from January 1987 to December 1988. Repeated scans of the operated area revealed a distinct increase in thickened ultrasonographic features (32% vs 8%), and a stenosing lesion was detected in 8 patients. There was also a parallel increase in the number of subjects with thicknesses of the intima adjacent to the endarterectomy area exceeding 2.5 mm. In 7% of cases, dilatation was detected in the operated area and in 27% the margin of the area was raised. The study also dealt with the contralateral carotid artery, where a progression of atheromatous involvement was observed with an increased number of cases of hemodynamically significant stenosis and 3 cases of occlusion. Periodic duplex ultrasonography in endarterectomized patients proves useful for the early detection of hemodynamically significant stenoses or of structural features potentially capable of generating emboli.