Although uncommon, borderline personality disorder (BPD) may manifest for the first time later in life. A retrospective clinical file audit was used to identify the clinical manifestation of BPD for the first time at or above the age of 30, and to examine whether particular clinical and psychosocial factors may be associated with a later‐in‐life manifestation of BPD. Twenty‐three cases of late manifestation BPD were identified. People with late manifestation of BPD had similar risk factors and vulnerabilities, including childhood trauma, to the broader BPD population. They were distinguished by having higher levels of education, employment, and long‐term intimate relationships. Interpersonal problems, loss of employment and reminders of past sexual trauma were key precipitating factors. The findings underscore the legitimacy of a late‐manifestation diagnosis of BPD by demonstrating that BPD does not present exclusively during adolescence and early adulthood. BPD may present for the first time in later life in response to loss of protective factors or triggering of past trauma. This understanding may reduce misdiagnosis or delayed diagnosis, prescription of inappropriate treatments or delays in receiving BPD‐appropriate treatments.