Isolated agenesis of the gallbladder (AG) is a rare anomaly. Twenty-three percent of the patients are symptomatic and present with right upper abdominal pain, nausea and fatty food intolerance. The condition is frequently mistaken with excluded or sclero-atrophic gallbladder, regardless of the imaging modality used. Consequently, AG leads often to unnecessary and potentially dangerous surgery. During laparoscopy, the absence of normal anatomical structures and the impossibility of pulling on the gallbladder to dissect the triangle of Callot represent an increased risk of iatrogenic injury to biliary or portal structures. The aim of this study is to discuss the pitfalls of the available radiological exams and the management of this rare condition. We describe two cases of AG, with a review of the literature. A high index of suspicion is necessary when interpreting the radiological images. In case of doubt, a MRI-cholangiography is mandatory. Because of possible inherited transmission, relatives with a history of biliary symptoms should be investigated, even when asymptomatic.