Atrial septal aneurysm can be detected by subcostal echocardiography as a bulge of the intermediate interatrial septum, ballooning toward the right atrium. We retrospectively revised 5412 echo examinations, consecutively performed in our laboratory, and we found 14 cases of atrial septal aneurysm (0.26%), mean age 36 +/- 15 years, 9 males and 5 females. In 7 patients atrial septal aneurysm was wide, including the whole atrial septum; in 5, only cranial two-thirds of the septum were involved and in 2, it regarded only the intermediate septum. No patients referred to arrhythmias, syncope, embolism, endocarditis or transient ischemic neurologic disorders. Cardiac abnormalities or defects were associated to atrial septal aneurysm in 12/14 patients: they consisted of atrial septal defect, mitral valve prolapse, false ventricular tendons or persistent Chiari network. Atrial left-to-right shunt was detected in all 6 cases with atrial communication. Considering each single associated cardiac abnormality, the prevalence of atrial septal aneurysm was 7% in patients with atrial septal defect, 1.7% in those with mitral valve prolapse, 6.6% in persistent Chiari network and 0.9% in false ventricular tendons. In conclusion, echocardiography is the first-choice technique to detect atrial septal aneurysm and other related cardiac defects.