Governments in Australasia are introducing emergency department length of stay (EDLOS) time targets similar to the UK ‘four hour rule’. There is debate about whether this rule had beneficial effects on health-care outcomes. We sought to determine what effects the four hour time target for EDLOS had on clinically relevant outcomes in the UK by conducting a systematic search for evidence. Articles were screened by both authors independently and assessed for quality using standard tools. Differences in outcomes measured and how they were measured precluded meta-analysis. There were inconsistencies between target achievement reported by Trusts and that reported in the studies, and empirical evidence that the target might be unattainable. National Health Service spending on ED increased £820 000 000.00 (1998–2007) and emergency admissions rose overall by 35% (2002–2006), but not in all hospitals. Time to see a treating clinician and hospital mortality was unchanged. One hospital demonstrated a small reduction in return rate. The impact of the introduction of an ED time target and the associated massive financial investment has not resulted in a consistent improvement in care with markedly varying effects being reported between hospitals. Countries seeking to emulate the UK experience should proceed with caution.