Three hundred eighty-one children with isolated VSD were catheterized from 1960 through 1985, 228 of whom were first catheterized in the first year of life. Defect size was defined by the right-to-left ventricular systolic pressure ratio. Patients with small VSD had a good outcome, with no pulmonary vascular disease. Seventy-five percent of patients with moderate VSDs did not require surgery, and 58% had normal pulmonary artery pressures documented on a second catheterization. Of those patients with large VSDs who underwent serial catheterizations in the first year of life before surgery, 62% had partial closure, and pulmonary vascular resistance rose in 21%. None developed pulmonary vascular disease after surgery. Fewer large-restrictive than nonrestrictive VSDs required surgery in infancy (12% vs 51%; p less than 0.005), and more closed enough to never require surgery (62% vs 27%; p less than 0.005, chi square). Surgery is rarely necessary for patients with small and moderate-sized VSDs in the first year and is usually never necessary because of the expected decrease in size. Few patients with large-restrictive VSDs have an increase in pulmonary vascular resistance, many defects decrease in size, and most patients never need surgery. Patients who have a nonrestrictive VSD have an excellent prognosis with appropriate management.