Objective. To examine associations between maternal Asian ethnicity (South Asian and South East/East Asian) and anal sphincter injury. Design. Retrospective cross-sectional study, comparing outcomes for Asian women with those of Australian and New Zealand women. Setting. A large metropolitan maternity service in Victoria, Australia. Population. Australian/New Zealand, South Asian and South East/East Asian women who had a singleton vaginal birth from 2006 to 2012. Methods. The relation between maternal ethnicity and anal sphincter injury was assessed by logistic regression, adjusting for potential confounders. Main outcome measures. Anal sphincter injury was defined as a third or fourth degree tear (with or without episiotomy). Results. Among 32 653 vaginal births there was a significant difference in the rate of anal sphincter injury by maternal region of birth (p <0.001). After adjustment for confounders, nulliparous women born in South Asian and South East/East Asia were 2.6 (95 confidence interval 2.2?3.3; p <0.001) and 2.1 (95 confidence interval (1.7?2.5; p <0.001) times more likely to sustain an anal sphincter injury than Australian/New Zealand women, respectively. Parous women born in South Asian and South East/East Asia were 2.4 (95 confidence interval 1.8?3.2;p <0.001) and 2.0 (95 confidence interval 1.5?2.7; p <0.001) times more likely to sustain an anal sphincter injury than Australian/New Zealand women, respectively. Conclusion. There are ethnic differences in the rates of anal sphincter injury not fully explained by known risk factors for such trauma. This may have implications for care provision.