There are few data on the outcome of truncus arteriosus when this diagnosis is made during fetal life. Such prognostic information is important to assist parental counseling during pregnancy. This study aimed to analyze, retrospectively, the echocardiographic features and outcome of fetuses with truncus arteriosus. A database of those presenting to a tertiary center for fetal cardiology between 1990 and 1999 was reviewed. Cases in which truncus arteriosus was identified as a firm or differential diagnosis were selected. Outcome data were derived from clinical records, and fetal echocardiograms were reviewed retrospectively. At presentation, truncus arteriosus was firmly diagnosed in 16 patients and was a differential diagnosis in 12. Fourteen of 16 (87%) of the firm diagnoses were correct. There were 17 confirmed cases of truncus arteriosus. Pregnancy was terminated in 4 patients (24%) and there were 13 live births. One child was not actively treated, 4 (31%) died preoperatively, and 8 (61%) underwent surgery. Thirty-day surgical mortality was 2 of 8 (25%). There was 1 late death after cardiac catheterization, and overall survival on an intention-to-treat basis was 5 of 12 (42%). Five of 6 patients with a prenatal truncal valve Doppler velocity above the normal aortic range were found to have postnatal truncal valve stenosis. Two fetuses with stenotic valves died preoperatively with sudden cardiovascular collapse. Counseling of parents for fetuses with truncus arteriosus should include the relatively high nonsurgical mortality as well as surgical results. Elevated prenatal truncal valve Doppler velocity predicts postnatal truncal valve stenosis. Fetuses with truncal valve stenosis may be at risk of early sudden death.