Agenesis of the gallbladder is a rare anomaly that is usually asymptomatic, but sometimes the patients may have symptoms compatible with a biliary disorder like cholelithiasis. Its preoperative diagnosis is often difficult, especially if dysplastic cyst is associated and simulates the gallbladder. When the diagnosis is doubtful its confirmation and treatment of dysplastic cyst require open surgery, careful dissection of the common bile duct to avoid biliary lesions and intraoperative ultrasonography or cholangiography to be performed to exclude other associated anomalies. The Authors describe the case of agenesis of gallbladder and dysplastic cyst associated and comment on its clinical, diagnostic, and therapeutic aspects.