OBJECTIVE: To present data on the epidemiology and spontaneous closure for septal defects (secundum atrial septal defect (ASD) and/or ventricular septal defect (VSD)). METHODS: Data from the EUROCAT Registry of Congenital Malformations for Funen County, Denmark were analyzed. All infants born from 1986 to 1998, diagnosed with a secundum ASD and/or a VSD as the only cardiac malformation, were included. RESULTS: There were 78 infants with an ASD, 195 with a VSD, and 19 had both an ASD and a VSD. The overall prevalence of septal defects was 4.1 per 1000 livebirths. Among the VSDs 45% were perimembranous and 55% were muscular defects. Associated non-cardiac malformations, syndromes, or karyotype anomalies were present in 54 cases (19% of total) but with a significantly lower proportion among cases with muscular VSDs (7%, p