This study was aimed at determining the predictive value of pre-operative signs in comparison with those of per-operative cholangiography in the diagnosis of an obstruction in the common bile duct during cholecystectomy for lithiasis. 154 cases were studied. The predictive value of pre-operative signs suggestive of obstruction was 0.46 and that of per-operative cholangiography 0.81. The predictive value of signs suggestive of the absence of obstruction was 0.90 and 1 for per-operative cholangiography. Per-operative cholangiography should thus be performed whenever possible during cholecystectomy for lithiasis.