The charts of 222 patients with a diagnosis of ventricular septal defect (VSD) were reviewed to determine the overall incidence, the prevalence of membranous and muscular defects and the rates of spontaneous VSD closure. VSD diagnosis and location were determined primarily from reports of 2-dimensional and pulsed Doppler echocardiograms. In a 5-year period, VSDs occurred in 3.85/1,000 live full-term births and 7.06/1,000 live premature births. The VSD closed spontaneously in 20 of 44 patients (45%) followed from birth (University Hospital group) during a mean follow-up of 12 months. Of 165 patients not followed from birth (referred group), the VSD closed spontaneously in 37 (22%). Overall, VSD location was determined in 101 of 209 patients (48%) and was distributed as follows: membranous 66 (65%), muscular 32 (32%) and subpulmonic 3 (3%). Rates of spontaneous closure for membranous and muscular VSDs were 37% and 50%, respectively, for the University Hospital group and 9% and 9%, respectively, for the referred group (no significant difference in either case). Surgical closure was required in 30 of 165 referred patients (18%) and only 1 of 44 University Hospital patients (2%). There was no significant difference in rate of closure for premature vs full-term infants or small vs larger defects. Data for patients followed from birth more likely reflect the true natural history of VSD.