INTRODUCTION AND BACKGROUND: About 1% of live-born children have congenital malformations of the heart. The aim of our study was to investigate the incidence of such defects in children born in Iceland during a period of 10 years, extending from 1990 through 1999. MATERIALS AND METHODS: Information about the patients was obtained from medical records from two hospitals that cover the whole country, a private clinic of pediatric cardiologists, an echocardiography database, autopsy reports, and death certificates. We investigated the distribution of specific malformations, the age at diagnosis, the symptoms leading to the diagnosis, the source of referral, and treatment and quality of life. RESULTS: Between 1990 and 1999, there were 44,013 live births in Iceland, of which 740 patients were diagnosed with congenital cardiac malformations, accounting for 1.7% of the live-born children. The distribution was made up of 338 patients with ventricular septal defect (45.7%), 90 with atrial septal defect (12.2%), 85 with patency of the arterial duct (11.5%), 48 with pulmonary valvar stenosis (6.5%), 38 with a bicuspid aortic valve (5.1%), 28 with aortic coarctation (3.8%), 22 with tetralogy of Fallot (3.0%), 14 with transposed great arteries (1.9%), 11 with aortic stenosis (1.5%), 10 with atrioventricular septal defect and common atrioventricular orifice (1.4%), 9 with mitral valvar regurgitation (1.2%), 7 with sub-aortic stenosis (0.9%), and 5 with hypoplasia of the left heart (0.7%). Extracardiac anomalies were seen in 89 patients (12.0%). Chromosomal defects were seen in 36 patients, of whom 28 had Down's syndrome. DISCUSSION: The annual incidence of diagnosis of patients with congenital cardiac malformations increased during the period of study. This was noted for minor defects, but the incidence of the major anomalies did not alter. Our observed yearly incidence, at 1.7%, was higher than noted in a previous study covering the years 1985 through 1989, and is also higher than in other population-based studies. The most likely explanation is the fact that access to pediatric cardiologists in Iceland is very good. Diagnosis, registration, and follow-up are conducted by only a few cardiologists, and take place at a single center for pediatric cardiology.