["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nThere is increasing recognition of the challenge of representativeness in data, including economic, social, and ethnic diversity, in biological mental health research. This is a particular challenge in adolescence, where brain and body development are impacted by the environment. The first step in addressing this is understanding the scale of the challenge. As such, this scoping review aims to explore existing literature to identify and understand the needs, barriers, and facilitators in collecting biological data in adolescent mental health research.\n\n\nMethods\nA systematic search identified papers recruiting participants aged 11–18, collecting biological data, and focussing on mental health/related psychopathology. Screening was performed in duplicate, and data charting was iterative.\n\n\nResults\nThe initial search identified 13,752 papers. After removal of duplicates and screening exclusions, 962 papers were included; 892 were explored for recruitment, retention, and engagement. Sample sizes <99 were most common (54.4%), and health settings (45%) were the most frequent recruitment source. As labels for ‘barriers’, ‘facilitators’, and ‘needs’ were rarely used, information on recruitment, retention, and engagement (e.g. strategies for stakeholder engagement) were explored as a proxy. Only 8.6% of papers reported engagement strategies; fewer evaluated their efficacy. Less than half (45.6%) reported retention data, with reasons for lost data mostly relating to the nature of the data collection.\n\n\nConclusions\nPapers do not adequately report the methods used to ensure sufficient collection of representative data. Limited reporting challenges whether or not facilitators are being implemented. Advancing the field requires detailed guidelines. We present recommendations that serve as a first step towards this development.\n\n"]