BackgroundNeonatal research evaluates many different outcomes using multiple measures. This can prevent synthesis of trial results in meta-analyses, and selected outcomes may not be relevant to former patients, parents and health professionals.ObjectiveTo define a core outcome set (COS) for research involving infants receiving neonatal care in a high-income setting.DesignOutcomes reported in neonatal trials and qualitative studies were systematically reviewed. Stakeholders were recruited for a three-round international Delphi survey. A consensus meeting was held to confirm the final COS, based on the survey results.ParticipantsFour hundred and fourteen former patients, parents, healthcare professionals and researchers took part in the eDelphi survey; 173 completed all three rounds. Sixteen stakeholders participated in the consensus meeting.ResultsThe literature reviews identified 104 outcomes; these were included in round 1. Participants proposed 10 additional outcomes; 114 outcomes were scored in rounds 2 and 3. Round 1 scores showed different stakeholder groups prioritised contrasting outcomes. Twelve outcomes were included in the final COS: survival, sepsis, necrotising enterocolitis, brain injury on imaging, general gross motor ability, general cognitive ability, quality of life, adverse events, visual impairment/blindness, hearing impairment/deafness, retinopathy of prematurity and chronic lung disease/bronchopulmonary dysplasia.Conclusions and relevanceA COS for clinical trials and other research studies involving infants receiving neonatal care in a high-income setting has been identified. This COS for neonatology will help standardise outcome selection in clinical trials and ensure these are relevant to those most affected by neonatal care.