TITLE The utility of non-rule based visual matching as a strategy to allow novices to achieve skin lesion diagnosis Funding from The Wellcome Trust (Reference 083928/Z/07/Z) and the Foundation for Skin Research (Edinburgh). RBA a and LB a supported by Wellcome Trust. ABSTRACT Non-analytical reasoning is thought to play a key role in dermatology diagnosis. Considering its potential importance, surprisingly little work has been done to research whether similar identification processes can be supported in non-experts. We describe a prototype diagnostic support software, which we have used to examine the ability of medical students (at the beginning and end of a dermatology attachment) and lay volunteers, to diagnose 12 images of common skin lesions. Overall the non-experts using the software had a diagnostic accuracy of 98% (923/936) compared to the control group of 33% (215/648) (Wilcoxon p<0.0001). We have demonstrated, within the constraints of a simplified clinical model, that novices' diagnostic scores are significantly increased by the use of a structured image database coupled with matching of index and referent images. The novices achieve this high degree of accuracy without any use of explicit definitions of likeness or rule-based strategies.