There are limited data about the distribution of atrial septal defect types in Turkey. In this study, morphological features of the cases diagnosed to have atrial septal defect by transesophageal echocardiography were compared. The study, designed as retrospectively, included 240 cases with atrial septal defect diagnosed by transesophageal echocardiography at two different clinics. In all patients transesophageal echocardiography was performed after routine transthoracic echocardiography. With transesophageal echocardiography, the presence and the type of atrial septal defect and accompanying cardiac abnormalities were determined. In statistical analysis, categorical variables were analyzed by Chi-square test, and continuous variables were analyzed by Kruskal-Wallis test. Mann-Whitney U test was used in intergroup comparisons. Mean age of the patients was 25±10 (15- 77) years, and female/male ratio was 30/210. Of the cases, 196 (82%) were ostium secundum type, 28 (%12) were sinus venosus type and 16 (7%) were ostium primum type. There were no significant differences among the types with regard to age and gender, and pulmonary artery pressure was higher in the ostium primum type. Pulmonary venous return abnormality was more common in sinus venosus type, and mitral regurgitation was present in all patients with ostium primum type. The most common acquired cardiac abnormality was tricuspid insufficiency. Our data are in quality of shedding light on young Turkish population.