AIMS: To investigate what patterns of bruising are diagnostic or suggestive of child abuse by means of a systematic review. METHODS: All language literature search 1951-2004. Included: studies that defined patterns of bruising in non-abused or abused children <18 years. Excluded: personal practice, review articles, single case reports, inadequate confirmation of abuse. Two independent full text reviews using standardised data extraction and critical appraisal forms. Studies ranked by study design and definition of abuse used. RESULTS: Twenty three studies included: seven non-abusive bruising, 14 abusive bruising, and two both. Non-abusive: The prevalence, number, and location of bruises is related to increased motor development. Bruising in non-independently mobile babies is very uncommon (<1%). Seventeen per cent of infants who are starting to mobilise, 53% of walkers, and the majority of schoolchildren have bruises. These are small, sustained over bony prominences, and found on the front of the body. Abuse: Bruising is common in children who are abused. Any part of the body is vulnerable. Bruises are away from bony prominences; the commonest site is head and neck (particularly face) followed by the buttocks, trunk, and arms. Bruises are large, commonly multiple, and occur in clusters. They are often associated with other injury types that may be older. Some bruises carry the imprint of the implement used. CONCLUSION: When abuse is suspected, bruising must be assessed in the context of medical, social, and developmental history, the explanation given, and the patterns of non-abusive bruising. Bruises in non-mobile infants, over soft tissue areas, that carry the imprint of an implement and multiple bruises of uniform shape are suggestive of abuse. Quality research across the whole spectrum of children is urgently needed.