CA19-9 serum has been suggested as a marker of unresectability but different cut-off levels have been published. A cut-off of 500 U/ml is currently considered in an international consensus as biological criteria of borderline resectable pancreatic adenocarcinoma. To evaluate whether serum CA19-9 threshold of 500 U/ml could be adequate predictor of resectability in pancreatic adenocarcinoma. Multicenter, observational, prospective study performed in Spain including 203 patients diagnosed with pancreatic adenocarcinoma. 43 (21.2%) cases were resectable and 160 (78.8%) unresectable. Among the 176 preoperative CA19-9 available values, 98 (58.3%) were ≤ 500 U/ml and 73 (42.7%) > 500 U/ml. Resectability rate in those patients with CA19-9 ≤ 500 U/ml was 60% while it was found to be 18% when CA19-9 > 500 U/ml. Statistical model to predict resectability based on CA19-9 provide an AUC of 0.6618 (95% CI 0.53-0.83) when only CA19-9 values > 500 U/ml are studied. Serum levels of CA19-9 higher than 500 U/ml are indicative of unresectable disease, however reduced sensitivity and specificity lead to a limited clinical applicability for resectability.