From 1951 to 1981 we evaluated 79 adult patients with ventricular septal defect with no other associated cardiac malformations. There were 42 men and 37 women ranging in age from 18 to 59 years (mean 34 years). We divided our patients into 67 patients treated medically and 12 surgically. Follow-up was obtained on 78 of 79 patients (99%). All patients were followed up for 1 month to 25 years (mean 9 years). Their ages at follow-up ranged from 24 to 70 years (mean 42 years). Nonsurgically treated patients who were New York Heart Association functional class I before treatment had a significantly better survival rate than had those who were functional class II to IV (p less than 0.001). Nonsurgically treated patients with cardiomegaly had a significantly poorer survival experience than had those without pretreatment cardiomegaly (p less than 0.001). Medical patients also had significantly poorer survival rates if the mean pulmonary artery systolic pressure was greater than 50 mm Hg (p less than 0.001). The 10-year survival rate for all patients was 76%. In general, adult patients with ventricular septal defect treated medically remained clinically stable over a long follow-up period, but survival was significantly influenced by pretreatment functional class, pulmonary artery systolic pressure, and cardiomegaly.