OBJECTIVES: A small number of cases of minor head injury deteriorate, resulting in serious injury or death. Computed Tomography (CT) identify intracranial injuries, but because it carries a cost and its own health risk, it should be limited to those most likely to have an injury. Clinical decision rules aim to identify these patients. There are many such rules, but it is unclear how their diagnostic accuracy compare. This study aimed to systematically identify clinical decision rules for adults with minor head injury and compare the estimated diagnostic accuracy. METHODS: Several key electronic bibliographic databases (biomedical, scientific and grey literature), were searched from inception to March 2010.  Retrieved citations were considered for inclusion by at least two independent reviewers. Cohort studies that described a clinical decision rule to identify adults with minor head injury (GCS 13-15) at risk of intracranial injury or injury requiring neurosurgical intervention were included in the review. Data was extracted by one reviewer and checked by a second. Studies were quality assessed using the QuADAS tool. RESULTS: Twenty-two relevant studies were identified. No study satisfied all quality assessment items. Heterogeneity amongst patient selection criteria, outcome definitions, and reference standards was identified. The Canadian CT Head Rule (CCHR) high-risk criteria had sensitivity of 99-100% with specificity of 48-77% for injury requiring neurosurgical intervention. Other rules, such as New Orleans criteria, NEXUS II, NCWFNS and SIGN produce similar sensitivities but with lower and more variable specificity values. CONCLUSIONS: The most widely researched decision rule is the CCHR, which has consistently shown high sensitivity for identifying injury requiring neurosurgical intervention, with an acceptable specificity to allow considered use of cranial CT. No other decision rule has been validated as widely, or demonstrated similarly acceptable results. However, its exclusion criteria mean it may make it difficult to apply universally.