Objectives: Describe outcomes among preterm infants diagnosed with single-vessel primary pulmonary vein stenosis (PPVS) initially treated using conservative management (active surveillance with deferral of treatment). Study design: Retrospective cohort study at a single, tertiary-center (2009–2019) among infants <37 weeks’ gestation with single-vessel PPVS. Infants were classified into two categories: disease progression and disease stabilization. Cardiopulmonary outcomes were examined, and a Kaplan–Meier survival analysis performed. Results: Twenty infants were included. Compared to infants in the stable group (0/10, 0%), all infants in the progressive group had development of at least severe stenosis or atresia (10/10, 100%; P< 0.01). Severe pulmonary hypertension at diagnosis was increased in the progressive (5/10, 50%) versus the stable group (0/10, 0%; P= 0.03). Survival was lower among infants in the progressive than the stable group (log-rank test, P< 0.01). Conclusion: Among preterm infants with single-vessel PPVS, risk stratification may be possible, wherein more targeted, individualized therapies could be applied.