Abstract.Background: In England and Wales, women in prison make up a minority (<5%) of the total custodial population, yet acts of self-harm are around five times more common among incarcerated women. While there has been a multiagency effort to improve how acts of self-harm are documented across prisons, the patterns and functions of self-harm for women in prison have not yet been fully addressed. Aims: We aimed to determine the patterns, prevalence, and functions of self-harm among women in prison through a mixed-methods study. Method: A total of 108 women with a history of self-harm were interviewed across three female prisons. Participants completed a structured questionnaire detailing their experiences of self-harm across prison and community settings. Results: We found that women in prison who frequently self-harmed disclosed high levels of trauma: past experiences of domestic violence (81.5%), childhood sexual abuse (66.7%), and adult sexual abuse (60.2%). Prevalent methods of recent in-prison acts of self-harm involved cutting, followed by ligaturing. Limitations: The study used a cross-sectional design, self-reported data, and featured a subset of women identified as being at high-risk of self-harm. Conclusion: Motivations behind acts of self-harm by women in prison are complex. Triggers appear to be past trauma, deteriorating mental health, and separation from children or family.