Objective and design. The Leiden Developmental Care Project explored the effects of the basic elements of developmental care (DC: the use of incubator covers and nests) and the Newborn Individualized Developmental Care and Assessment Program (NIDCAP) with individual behavior observations for very premature infants less than 32 weeks of gestation. Design. Two consecutive randomized trials in two Dutch neonatal intensive care units: standard care versus DC and DC versus NIDCAP care. Method. Questionnaires completed by parents during admission (parental stress and confidence and social support) and follow-up at 1 year of corrected age (parental stress, behavior and health-related quality of life of the children) and by caregivers after implementation of the NIDCAP. Results. Quality of life and parental stress were not influenced by either type of intervention. Limited effects were found on competence child behavior at 1 year of age, when children who had received DC showed more mastery motivation (curiosity, persistence and obedience). When the intervention duration was longer, the behavioral observations had a positive effect on the social relatedness behavior of the children at 1 year. Parents, nursing and (para)medical personnel in the neonatal unit reported a positive effect of NIDCAP care on comfort and well-being of the children during admission to the neonatal unit. Conclusion. Although only limited effects on outcome were found, parents and personnel in the neonatal units were positive about the effects of the interventions on comfort and well-being of the very premature infants. A complete cost-benefit analysis in the Dutch setting is important because of the high training costs of the NIDCAP. Future research should consider a longer intervention duration, use of comfort or pain measures and a qualitative evaluation by parents and caregiving personnel.