79 Medical decision‑making competence regarding puberty suppression: perceptions of transgender adolescents, their parents and clinicians 5 MDC describes the capacities that a person needs to make an autonomous medical decision (Grisso et al., 1997). To have MDC, one needs to fulfil the following four criteria: (1) understanding the information relevant to one’s condition and the proposed treatment; (2) appreciating the information and relating it to one’s circumstances including one’s current medical situation and one’s values; (3) reasoning about benefits and potential risks of the options; and (4) communicating a choice (Appelbaum & Grisso, 1988). MDC is relative to a specific decision and context. It is one of the three prerequisites to give valid informed consent, besides being well-informed and without coercion (Beauchamp & Childress, 2008; Grisso & Appelbaum, 1995). In December 2020, the High Court of Justice in London ruled that transgender minors under the age of 16 are highly unlikely to fully understand the long-term effects of PS, and therefore are not competent to decide on treatment with PS (Dyer, 2020a). As a result of this verdict transgender adolescents in England could no longer start PS before age 16 unless a court order was obtained (Dyer, 2020b). However, in September 2021 the Court of Appeal overturned the High Court’s ruling of December 2020 (Thornton, 2021). Furthermore, in Sweden paediatric endocrinologists stopped providing PS to newly referred transgender adolescents in May 2021 because of, among others, concerns regarding harmful long-term consequences (Naiingolan, 2021). In summary, adolescents’ MDC to start PS is and has been under discussion for some time among both advocates and opponents of the use of PS in transgender adolescents (e.g. Armitage, 2021; de Vries et al., 2021; Moreton, 2021; Pang et al., 2021; Wheeler, 2021). Adolescents’ MDC has often proved difficult to assess and is usually evaluated implicitly in clinical settings (Hein et al., 2015b). Additionally, there is little empirical evidence on transgender adolescents’ competence to decide on PS. To our knowledge, there is only one study, from the Netherlands performed in our centres, that has examined this by a structured replicable interview. That study shows that the vast majority (89%) of transgender adolescents (aged 10-18 years) about to start PS treatment are competent to consent to this treatment (Vrouenraets et al., 2022b). Little research has examined the ideas and considerations of adolescents themselves and their parents regarding adolescents’ MDC to start PS. An interview study showed that clinicians stated that they find it important that the adolescentsmature a little further during the period they receive PS so that they will be better able to decide about proceeding to GAH and carefully consider their decision’s consequences. This implies that these clinicians assume that the adolescents, when they decide on PS, are not always competent yet to decide on GAH (Vrouenraets et al., 2022b). Insight into the stakeholders’ perceptions of adolescents’ MDC will help to further improve care and support for adolescents in their decision-making process. Therefore, we performed an interview and focus group study to