We compared the intra-operative diagnostic value of CDS vs IA-DSA in identifying major and minor technical defects after CEA. Between August 1997 and December 1998, 138 consecutive patients undergoing 141 carotid endarterectomies were intra-operatively investigated with colour duplex scan and intra-arterial digital subtraction angiography. Thirty-six (25.5%) technical defects were identified. Four (11.1%) major defects were detected by both methods and they were immediately corrected. Fifteen (41.6%) minor defects were detected by both methods, thirteen (36.1%) minor defects were detected by colour duplex but ignored by angiography. Angiography detected four (11.1%) kinkings missed with the colour duplex. The overall sensitivity of both methods for major defect was 100%. The sensitivity of colour duplex for minor defects was 87% vs 59% for angiography. On the basis of our study, colour duplex could be considered the choice method for quality control after carotid endarterectomy.