Congenital anomalies in the adult thorax are frequently asymptomatic and may remain undetected for many years. Whether they then become symptomatic or are discovered as an incidental finding on an imaging study obtained for unrelated reasons, thoracic anomalies may appear as masses or contour abnormalities that mimic other pathology, particularly neoplastic disease. The aim of this review is to discuss and illustrate a wide variety of congenital thoracic anomalies that can potentially present as a mass in the thorax. For ease of discussion, lesions are classified under numerous headings, including congenital lung anomalies caused by bronchopulmonary malformations and anomalies of pulmonary vasculature, vascular anomalies of the great vessels, diaphragmatic anomalies, and congenital masses of the chest wall. The appearance of these congenital lesions on chest radiographs and other imaging modalities such as CT, MRI, and angiography are illustrated, with emphasis on features that can distinguish these lesions from other intrathoracic masses.