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 < 0.005), and more closed enough to never require surgery (62% vs 27%; p < 0.005, chi square). Surgery is rarely necessary for patients with small and moderatesized 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.