Atrial septum aneurysm (ASA) is an uncommon congenital malformation, which is more frequently diagnosed since the introduction of transoesophageal echocardiography. ASA is often involved in the etiology of cerebral and systemic embolic events. The purpose of our study is to determine from our experience the frequency, the diagnostic aspect and therapeutic modalities of ASA. We report in this study 20 cases of ASA collected from the echocardiographic register. The prevalence of this malformation is 0.08%, with a high male predominance. The mean age was 51 years. ASA was detected after brain embolism in 55% of cases. The diagnosis was established in all cases by transesophageal echocardiography, however only 5 cases were diagnosed by Transthoracic echocardiography. The patients showed favorable evolutions after a of follow up of three years.