<b><i>Purpose:</i></b> To assess the intrauterine course, the outcome, and to establish a new prenatal echocardiographic scoring system to predict biventricular (BV) versus univentricular (UV) outcome of fetuses with severe pulmonary stenosis or atresia with intact ventricular septum (PSAIVS). <b><i>Methods:</i></b> All cases of PSAIVS diagnosed prenatally over a period of 14<i></i>years were retrospectively collected in 2 tertiary referral centers. <b><i>Results:</i></b> Forty-nine fetuses with PSIVS (<i>n</i> = 11) or PAIVS (<i>n</i> = 38) were identified prenatally. Nineteen (38.8%) fetuses had additional ventriculocoronary connections (VCCs) and 21 (42.9%) fetuses had right ventricular hypoplasia. Four (8.2%) pregnancies were terminated, 2 (4.1%) ended in intrauterine fetal death, 4 (8.2%) in neonatal death, and 5 (10.2%) children died in infancy or childhood, including one case with compassionate care. Thirty-four of 44 (77.3%) fetuses with the intention-to-treat were alive at latest follow-up, 25 (73.5%) with BV, and 9 (26.5%) with UV circulation. Most significant predictive markers of UV circulation were Vmax of tricuspid regurgitation (TR) &#x3c;2 m/s, right ventricle/left ventricle length ratio ≤0.6, and presence of VCC. A scoring system including these 3 markers had 100% sensitivity and 100% specificity predicting an UV outcome if more than one of these criteria was fulfilled. All 25 liveborn infants that were suitable for BV repair survived, whereas only 9 out of 14 candidates for UV repair survived. None of the 14 fetuses with predicted UV outcome would have met the inclusion criteria for fetal intervention, as 10 of them had VCC and the remaining 4 had absent TR or Vmax &#x3c;2 m/s. <b><i>Conclusion:</i></b> The prognosis of prenatally diagnosed PSAIVS is good if BV circulation can be achieved, while postnatal mortality in UV circulation is high within the first 4 months of life. Postnatal outcome can be predicted prenatally with high accuracy using a simple scoring system. This information is mandatory for parental counseling and may be useful in selecting fetuses for intrauterine valvuloplasty.