Hypodontia is the failure of developmental of one or more teeth, resulting in their permanent absence. Different treatment options exist and decision-making requires collaboration between adolescents, parents and the dental team. Currently there is little evidence about decision-making practice and patient preferences for care. Aim: To examine adolescent and parent decision-making and preferences in hypodontia Design: Mixed methods Population & setting: Adolescents (aged 12-16 years) with hypodontia and their parents in NHS Hospitals in England and Wales Methods: Stage One: Examination of hypodontia care using mixed methods (systematic review of hypodontia literature, analysis of patient information resources and social media, observation of clinical consultations, interviews with adolescents and parents) to establish current decision-making practice. Stage Two: Development of a preference elicitation instrument for adolescents and parents, using Discrete Choice Experiment (DCE) tasks to examine decision-making processes and elicit preferences. Piloting used 'Think aloud' methods and verbal probing to test the validity and acceptability of the tool and methods. Stage Three: Preference elicitation survey with two approaches: 1) Online survey of adolescents and parents 2) Face-to-face survey completion by adolescent-parent dyads under observation to examine joint decision-making. Results: Adolescent and parent understanding of hypodontia and its treatment is limited. The current pathway does not promote collaborative decision-making and adolescent and parent participation in care decisions is low. Appearance after treatment, severe dental problems, severe discomfort during treatment and a long treatment time are important to decision-making. Individuals show important heterogeneity in preferences. Trade-offs tasks appeared to help some adolescents and parents think about care and understand what is important to them. Conclusions: Hypodontia care decisions require a collaborative approach, with appropriate information exchange about risks, benefits and outcomes with inclusion of patient preferences. Trade-off tasks might be useful in future decision support tools to help adolescents and parents think about treatment.