PROJECT SUMMARY/ABSTRACT This renewal application seeks NICHD support for 5 first-year and 5 second-year positions in the Pediatric Scientist Development Program (PSDP), a career development pathway for pediatric fellows from which 192 physician-scientists have graduated since 1987. The objectives of the program remain unchanged since its inception: (a) to recruit pediatric fellows whose outstanding potential for a successful investigative career can be developed in an intensively mentored setting and (b) to expand the pipeline of superbly trained pediatric physician-scientists, who will catalyze cutting-edge discoveries in child health and lead the pediatric departments of the future. Unique aspects of the PSDP include its North American scope for recruitment of fellows and mentors, its intensive focus on career development during fellowship, its supra-institutional governance under the aegis of the Association of Medical School Pediatric Department Chairs (AMSPDC), its emphasis on research environments outside departments of pediatrics, and its approach to mentoring that encompasses research mentors, PSDP advisory committees, and pediatric department chairs. Advisory Committees include a Steering Committee, which sets programmatic policy; a Selection Committee to interview PSDP candidates; and an independent Program Evaluation Committee measures the program’s effectiveness in ensuring fellows’ success. A centerpiece of the PSDP is the annual career development curriculum that convenes PSDP fellows, advisory committees, and all US and Canadian pediatric department chairs at the AMSPDC meeting. PSDP graduates have served as PIs on 335 NIH RPGs, of which 53% are currently active. Based on total awards of NIH RPGs with PSDP graduates are PIs, the return on NICHD investment is 8.8 fold. Innovations for 2017-2021 include a) leveraging NICHD funding by incorporating departmental support for up to 5 third-year fellows who will be appointed as instructors with 75-80% protected research time and b) expanding our career development curriculum with adult-learning educational modules that emphasize the fellow-to-faculty transition and team science, presented on site at AMSPDC and through web-based case-based studies. The PSDP has implemented a comprehensive strategy to expand the boundaries of child health research, to develop the research careers of rigorously trained pediatric physician-scientists, and to produce the next generation of investigative leaders in pediatrics.