Objective: To assess the association of mode of conception and sex concordance with neonatal outcomes in very preterm twins. Study design: Twin pairs born at gestational age ≤32 weeks and admitted to a Level 3 neonatal intensive care unit (NICU) in 2010–2011 were retrospectively identified from the Canadian Neonatal Network™ database. A composite outcome representing neonatal mortality or any severe morbidity (intraventricular hemorrhage grades ≥3 or periventricular leukomalacia, retinopathy of prematurity stages ≥3, bronchopulmonary dysplasia, or necrotizing enterocolitis stages ≥2) was compared between twins conceived using assisted reproduction technologies (ARTs) or spontaneously (SP), and tested for association with sex concordance in individual-level and pair-wise multivariable logistic regression analyses. Results: Study subjects included 1,508 twins from 216 ART (53 [25%] male–male, 104 [48%] male–female, and 59 [27%] female–female) and 538 SP (192 [36%] male–male, 123 [23%] male–female, and 223 [41%] female–female) pairs. No statistically significant association was detected between mode of conception and the composite outcome of mortality/morbidities. The composite outcome was significantly higher in same-sex than in opposite-sex twins (OR = 1.68; 95% CI = [1.09, 2.59]). This relationship was most pronounced in ART pairs (OR = 2.25; 95% CI = [1.02, 4.98]), with increased rates in one or both twins from male–male versus opposite-sex ART pairs (OR = 3.0; 95% CI = [1.07, 8.36]). Conclusion: Same-sex pairing was associated with higher mortality/morbidities in very preterm twins admitted to the NICU, and can be used in clinical practice to identify twins at higher risk of adverse neonatal outcomes.