Background: Approximately one-third of young people in the UK have suffered intimate partner violence and abuse (IPVA) on reaching adulthood. We need interventions to prevent IPVA in this population, but there is a lack of evidence on who is at greatest risk. Methods: We used data from the Avon Longitudinal Study of Parents and Children population-based birth cohort. At age 22, 3,279 participants provided information on experiences of IPVA. We estimated the prevalence of IPVA victimisation and perpetration before age 18 and at 18-22 years, for men and women, and by characteristics previously identified as risk factors in other age-groups or non-UK populations: demographic characteristics, extreme parental monitoring, mental health conditions, externalising behaviours (e.g. regular smoking), no-low education/employment, adverse childhood experiences. Findings: 29% of men and 41% of women reported IPVA victimisation respectively, 20% and 25% perpetration (16% and 22% both). The most common IPVA sub-type was emotional, followed by physical, then sexual. Experiencing self-harm, anti-social behaviours, cannabis use, or illicit (non-cannabis) drug use was associated with a two-fold increase in likelihood of IPVA exposure (victimisation or perpetration) in men and women. Men reporting risky sexual behaviour, sexual abuse (not by an intimate partner), or witnessing domestic violence, and women reporting sexual minority status in adolescence were also twice as likely to experience IPVA. High levels of parental monitoring during adolescence was associated with a reduced risk of IPVA exposure in men and women, as was not being in education, employment, or training in young adult men. Interpretation: At least one in three young adults were either victimised or perpetrated IPVA, and a range of demographic, mental health, and behavioural risk factors were associated with increased prevalence. Further study of likely complex pathways from these factors to IPVA, to inform primary prevention, is needed. Funding Statement: Medical Research Council (MR/S002634/1). AF and LDH are funded by MRC personal fellowships (MR/M009351/1, MR/M020894/1). Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: Ethical approval for the study was obtained from the ALSPAC Law and Ethics Committee and the Local Research Ethics Committees (proposal B1316). Informed consent for the use of data collected via questionnaires and clinics was obtained from participants following the recommendations of the ALSPAC Ethics and Law Committee at the time.