Obstetric brachial plexus injury (OBPI) is uncommon but accounts for a significant proportion of obstetric clinical negligence claims. There is debate in the medical literature and in legal proceedings regarding the causation of OBPI, particularly whether OBPI is caused by the accoucheur applying excessive traction or simply through the forces of labour itself.This paper reviews the medical literature and legal case law surrounding OBPI and presents a template for reviewing the strength of evidence for OBPI in clinical negligence claims. The template contains factors more likely to be present if the OBPI was caused by the maternal forces of labour 'propulsion injury' (injury to the posterior arm, no documented evidence of shoulder dystocia, up-todate training, appropriate shoulder dystocia management, no evidence of excessive traction, correct number of birth attendants, precipitous second stage, temporary injury) and factors more likely if the injury is iatrogenic (injury to the anterior arm, shoulder dystocia, no recent training, incorrect shoulder dystocia resolution manoeuvres used, evidence of excessive traction, insufficient birth attendants, fundal pressure, permanent injury). Each factor does not, in itself, establish causation, but the template may provide a useful aid to legal teams reviewing medical notes.