Choledochal cyst is a relatively rare condition. Even rarer is a choledochal cyst in association with a gallbladder carcinoma. This study reports a rare case of gallbladder carcinoma coexisting with a choledochal cyst in a Nigerian patient. Clinical records of the patient including preoperative evaluation, intraoperative findings, and postoperative care were reviewed. A 38-year-old woman presented with the recurrent right upper abdominal pain of 3 years duration associated with progressive weight loss, anorexia, recurrent vomiting, as well as, low-grade fever with chills and rigors. Physical examination revealed an anicteric woman with tenderness in the right hypochondrium and a positive Murphy's sign. A combination of abdominal ultrasound and computed tomography scan suggested a Type IV choledochal cyst and a distended gallbladder with thickened walls containing a heterogeneous hyperdense mass. Preoperative serum alkaline phosphatase was elevated while endoscopic retrograde cholangiopancreatography was inconclusive. At laparotomy, extrahepatic biliary dilatation and enlarged, the nodular gallbladder was found with a diffusely fibrotic pancreas. Intraoperative cholangiogram confirmed Type IV choledochal cyst. Excision of the common bile duct and radical cholecystectomy was performed, and a Roux-en-Y hepaticojejunostomy. Histopathology confirmed the diagnosis of gallbladder adenocarcinoma. She had adjuvant chemotherapy and is presently on follow-up. No evidence of recurrence after 5 years of follow-up. A high index of suspicion is required to detect a combination of these two rare entities. When detected, both conditions should be surgically addressed at the same sitting, and when combined with adjuvant chemotherapy, may increase the chances of achieving a cure.