Abdominal computed tomography (CT) is frequently performed to evaluate gastrointestinal pathologic conditions, and the majority of the gastrointestinal radiology literature has concentrated on the colon, stomach, and distal small bowel. In a description of CT findings of duodenal pathologic conditions, congenital, traumatic, inflammatory, and neoplastic diseases are presented. Congenital duodenal anomalies such as duplications and diverticula are usually asymptomatic, while annular pancreas and malrotation may manifest in the 1st decade of life. CT plays a vital role in the diagnosis of traumatic duodenal injury. Primary inflammatory processes of the duodenum such as ulcers and secondary involvement from pancreatitis can reliably be diagnosed at CT. Infectious diseases of the duodenum are difficult to diagnose, as the findings are not specific. While small bowel malignancies are relatively rare, lipoma, adenoma, and adenocarcinoma, as well as local extension from adjacent malignancies, can be diagnosed at CT. Careful CT technique and attention to the duodenum can result in reliable prospective diagnoses.