AbstractBackgroundGrowing evidence suggests that self‐harm‐related mental imagery is involved in the transition from self‐harm ideation to enactment. However, there has been little research on this important phenomenon in adolescent populations.MethodsUsing an online questionnaire, the frequency, content and impact of self‐harm‐related mental imagery was investigated in a transdiagnostic clinical population of young people with recent self‐harm. Mood ratings were used to assess the impact of completing the questionnaire.ResultsFifty‐five young people aged 14–24 years old completed the study. Participants were mostly female (85.5%) and White (87.3%). All but one participant (98.2%) reported images related to self‐harm, with 53 (96.4%) reporting future‐oriented self‐harm images, 53 (96.4%) reporting past‐oriented images, and 52 (94.5%) reporting both. Imagery included imagining self‐harm and particularly dangerous acts (including suicide), specific methods, and the consequences of self‐harm for self and others. Past self‐harm‐related mental imagery was sometimes used to develop future‐oriented self‐harm‐related imagery planning, highlighting the influence of previous exposure to self‐harm. Most participants (N = 45; 88.2%) stated that significant self‐harm‐related mental imagery increased the likelihood they would self‐harm. Stimulation of mental imagery was most frequently reported to be related to dreams about self‐harm (N = 33; 60.0%), and exposure to self‐harm‐related content on social media (N = 32; 58.2%) and in fictional TV programmes (N = 30; 54.6%). There was no significant difference in participants' pre‐ and post‐questionnaire mood ratings.ConclusionsSelf‐harm‐related mental imagery is commonly experienced by young people who self‐harm and may play a role in ideation‐to‐enactment of self‐harm. Asking about self‐harm‐related mental imagery can be done safely and could be considered for inclusion in routine clinical assessments. Self‐harm exposure and the origins of self‐harm‐related imagery, such as the links with past self‐harm and social media, as well as potential imagery‐based interventions for self‐harm, require further evaluation. A working model of self‐harm‐related mental imagery is presented.