Atrial septal defect (ASD) is the most common congenital cardiac anomaly manifested in adulthood. Clinical and radiographic features are well defined in patients less than 30 years of age. In older patients, however, the clinical symptoms are often atypical, and the auscultatory findings may be misleading. The radiographic manifestations in older patients have not been well described. In the current study, of 70 patients over the age of 50 years with proved ASD, 21 (30%) had atypical radiographic features, including apparently normal vascularity, left atrial enlargement, pulmonary venous hypertension, and pulmonary edema. In a control group of 70 younger patients with ASD, only 5.7% had atypical findings. The development of pulmonary venous hypertension and pulmonary edema in older patients was associated with smaller defects and a higher prevalence of mitral valve disease, left ventricular dysfunction, and pulmonary arterial hypertension than seen in older patients with typical radiographic findings.