PURPOSE: Despite the increasing focus on early parent-delivered interventions in neonatal intensive care units to enhance infant development, there remains a research gap concerning the sustained benefits of such interventions in preterm infants. This study evaluated the impact of the parent-administered sensorimotor intervention (PASI) on developmental outcomes of infants previously enrolled in a randomized clinical trial (RCT). METHOD: A prospective longitudinal follow-up study following the RCT at 4 and 18 months corrected gestational age (CGA) was conducted. A blinded examiner conducted the follow-up assessments. The study outcomes developmental outcome at both time points and the child's health-related quality of life at 18 months CGA using various means: Test of Infant Motor Performance (TIMP), the Feeding and Developmental Milestone Questionnaire (FDM), diagnosis of severe neurological disorder, the Infant Development Inventory (IDI) and Pediatric Quality of Life Inventory (PedsQL). RESULTS: At 4 months CGA, 47 infants participated in the follow-up, with more infants in the experimental group receiving direct breastfeeds compared to the control group (38 % vs. 12 %, p = 0.032). At 18 months CGA, 51 infants were followed, showing no significant differences in developmental outcomes or health-related quality of life between groups. However, more parents in the control group reported developmental concerns about their child compared to those in the experimental group. CONCLUSION: The PASI appears to have lasting positive effects on breastfeeding outcomes for infants and on parents' perceptions of developmental concerns. These findings underscore the importance of early postnatal experiences in influencing the long-term developmental trajectories of infants born preterm.