BACKGROUND: Limited data exist regarding the neonatal and neurodevelopmental outcomes of infants exposed to marijuana (MJ) in-utero, particularly among preterm infants. We hypothesized that MJ-exposed preterm infants would have worse neonatal and childhood developmental outcomes compared to MJ-unexposed infants. METHODS: Secondary analysis of multicenter randomized-controlled trial of antenatal magnesium sulfate for the prevention of cerebral palsy was conducted. Singleton nonanomalous infants delivered <35 weeks exposed to MJ in-utero were compared to MJ-unexposed. Primary neonatal outcome was death, grade 3/4 intraventricular hemorrhage, periventricular leukomalacia, bronchopulmonary dysplasia, and/or stage II/III necrotizing enterocolitis before discharge. Primary childhood outcome was death, moderate/severe cerebral palsy, or/and Bayley II Scales <70 at age 2. Backward-stepwise regression used to estimate odds of primary outcomes. RESULTS: 1867 infants met inclusion criteria; 135(7.2%) were MJ-exposed. There were no differences in neonatal (20% vs. 26%, p = 0.14) or childhood (26% vs. 21%, p = 0.21) outcomes in MJ-exposed infants compared to MJ-unexposed infants. In adjusted models, MJ-exposure was not associated with adverse neonatal outcomes (aOR 0.83 95% CI 0.47,1.44) or early childhood outcomes (aOR 1.47, 95% CI 0.97,2.23). CONCLUSIONS: Among infants born <35 weeks of gestation, MJ-exposure was not associated with adverse neonatal or childhood outcomes. Long-term follow-up studies are needed to assess later childhood neurodevelopmental outcomes following MJ-exposure.