Anal sphincter injury during childbirth is a leading cause of anal incontinence. In a study of more than 20 000 consecutive vaginal deliveries, clinically diagnosed obstetric anal sphincter injury occurred in 2.9% of primiparous women and 0.8% of multiparous ones.1 Of women who have sustained such an injury, 60-80% are asymptomatic at 12 months, of whom most report incontinence of flatus only, rather than faeces.2 ^{w1 w2} Establishing a correct diagnosis at time of injury will facilitate adequate repair and may prevent future incontinence.3 In one epidemiological study, only a third of people with faecal incontinence had ever discussed the problem with a doctor because of embarrassment or fear of stigma.4 This review outlines the determinants, diagnosis, and management of obstetric anal sphincter injury. Women affected by obstetric anal sphincter injury require acute management at the time of delivery, together with follow-up or referral when newly presenting with symptoms months or years after childbirth. This review is relevant to all who provide care during childbirth and to doctors and healthcare professionals to whom women may subsequently present.