Data on adult congenital heart diseases (CHD) are limited in Turkey. We evaluated the types and clinical features of CHDs in adult patients followed-up in our center.This study included 200 adult patients (age >16 years) who were diagnosed as having CHD in our clinic between April 2006 and January 2009. The patients were evaluated in three groups based on the complexity of adult CHD (simple, moderate, or great) according to the most recent ACC/AHA guidelines.There were 121 females (60.5%) and 79 males (39.5%). The mean age was 34.7+/-13.4 years (range 16 to 75 years) and female-to-male ratio was 1.53. The mean age was 32.8+/-14.0 years in males, and 36.0+/-12.9 in females. Nearly half of the patients were in the age groups of 20-29 years (n=46, 23%) and 30-39 years (n=49, 24.5%). According to the ACC/AHA criteria, 145 patients (72.5%) had simple CHD, 34 patients (17%) had moderate CHD, and 21 patients (10.5%) had severe-complex CHD. The mean age tended to decrease as the severity of CHD increased (35.7+/-13.7, 33.2+/-12.4, and 30.5+/-12.2 years, respectively). The most common adult CHD was atrial septal defect (n=105, 52.5%), followed by ventricular septal defect (n=34, 17%), Ebstein's anomaly (n=7, 3.5%), and Eisenmenger's syndrome (n=6, 3%). Aortic coarctation, transposition of the great vessels, patent foramen ovale, pulmonary stenosis, and aortic valve disease showed equal distribution with five patients (2.5%).In our study, atrial and ventricular septal defects accounted for the majority of CHDs in adult patients (69.5%). Multicenter studies are required to determine the incidence of CHD among adult population in Turkey.