Objective. To determine the prevalence and describe the clinical and echocardiographic characteristics of adults with atrial septal aneurysm (ASA). Materials and methods. A cross-sectional, descriptive study was conducted. The population consisted of patients diagnosed with ASA by transthoracic echocardiography. Results. The prevalence was 2%. The median age was 71 years, and females predominated (58.8%). ASA with right bulging represented 74.8%. The most frequent comorbidity was hypertension (64.1%). Atrial tachyarrhythmias were the most prevalent arrhythmias, and the most common valvular disease was mitral regurgitation (26.7%). Conclusions. The prevalence of ASA was similar to that reported in the literature; females predominated, the most prevalent comorbidity was hypertension, atrial tachyarrhythmias were the most frequent arrhythmias, ASA with right bulging was the most common, and...