This study investigates the sex-specific associations between early-life pain exposure, neonatal brain structural connectivity, and 18-month neurodevelopmental outcomes in preterm infants. The study included 193 very preterm infants from two tertiary neonatal intensive care units in Toronto, Canada, with structural connectivity data available for 150 infants and neurodevelopmental outcomes for 123 infants. Pain exposure was quantified as the total number of invasive procedures in the initial weeks after birth. Structural connectivity was assessed using diffusion tensor imaging, and neurodevelopmental outcomes were evaluated using the Bayley Scales of Infant and Toddler Development, Third Edition. Key findings include: - Greater early-life pain exposure was associated with slower maturation of global and local efficiency in female infants, but not in male infants. - In the full cohort, greater pain exposure was associated with lower global and local efficiency and regional connection strength. - Regional connection strength in the striatum was associated with cognitive outcomes. - Structural connectivity alterations were associated with poorer neurodevelopmental outcomes. The study highlights the importance of minimizing and adequately treating pain in preterm infants, particularly in female infants, and suggests that clinical trials of analgesic strategies should consider sex-specific effects.This study investigates the sex-specific associations between early-life pain exposure, neonatal brain structural connectivity, and 18-month neurodevelopmental outcomes in preterm infants. The study included 193 very preterm infants from two tertiary neonatal intensive care units in Toronto, Canada, with structural connectivity data available for 150 infants and neurodevelopmental outcomes for 123 infants. Pain exposure was quantified as the total number of invasive procedures in the initial weeks after birth. Structural connectivity was assessed using diffusion tensor imaging, and neurodevelopmental outcomes were evaluated using the Bayley Scales of Infant and Toddler Development, Third Edition. Key findings include: - Greater early-life pain exposure was associated with slower maturation of global and local efficiency in female infants, but not in male infants. - In the full cohort, greater pain exposure was associated with lower global and local efficiency and regional connection strength. - Regional connection strength in the striatum was associated with cognitive outcomes. - Structural connectivity alterations were associated with poorer neurodevelopmental outcomes. The study highlights the importance of minimizing and adequately treating pain in preterm infants, particularly in female infants, and suggests that clinical trials of analgesic strategies should consider sex-specific effects.