Brin F. S. Grenyer

Borderline personality disorder (BPD) is a severe mental health condition marked by impairments in self and interpersonal functioning. Stigma from health staff may often result in a reluctance to diagnose, impacting recovery trajectories. Qualitative interviews were conducted with participants ( N = 15; M Age = 36.4 years, SD = 7.5; 93.3% female) with lived experience of BPD exploring topics of illness onset, insight, experience of diagnosis and treatment. Qualitative responses were analysed within a co‐design framework with a member of the research team who identifies as having a lived experience of BPD. On average, participant symptoms emerged at 12.1 years of age ( SD = 6.6 years, range 1.5–27), but diagnoses of BPD were delayed until 30.2 years ( SD = 7.8 years, range 18–44) resulting in a ‘diagnosis gap’ of 18.1 years ( SD = 9.6 years, range 3–30). Participant explanations for BPD emergence varied from biological, psychological and social factors. Benefits of diagnosis (e.g., fostering insight, aiding treatment planning and reducing isolation) were contrasted with challenges (e.g., stigma and treatment unavailability). Delay in diagnosis was common, and no participants reported receiving a diagnosis of BPD during their adolescence yet 85% felt they would have benefited from a diagnosis in adolescence. Only a quarter (27%) felt highly supported in the diagnostic process. An ideal four‐step diagnosis procedure was outlined based on recommendations from participants with a lived experience; this involved the following: (1) explain the process, (2) assess thoroughly, (3) explore how the features are active in everyday life and (4) link diagnosis to evidence‐based treatment planning.