A 71-year-old man presented with painful obstructive jaundice, weight loss and an elevated CA19-9 (>16,000 U/ml) (normal levels <39 U/ml). Imaging showed a hilar mass. After biliary stenting, the CA19-9 returned to normal. At surgery, biliary obstruction owing to a gallstone (Type II Mirizzi) was found to be complicating a congenital biliary tract anomaly. The obstructing stone was removed and the anomalous biliary tract reconstructed with a Roux-en-y loop, and the patient made an uneventful recovery and remained normal over a 2-year follow-up. A Type II Mirizzi with a biliary tract anomaly is an undocumented cause of an elevated CA19-9. The possibility of benign disease must be considered even with very high levels of the cancer marker CA19-9 or the opportunity for curative surgery may be missed.