Melanoma of the skin is an increasingly common tumour, which often has a slow early growth rate during which curable lesions may be detected and removed. Physicians therefore have the potential to reduce mortality and this guideline is intended to promote early diagnosis of melanoma. The majority of melanomas occur in white-skinned people. The most common risk factors are pale sun-sensitive skin and the presence of increased numbers of melanocytic naevi (moles). Melanoma is more common in women than men; the mean age of onset is 50 years; and a fifth of cases occur in young adults. In the UK population the most common sites are on the lower leg in women, and on the back in men. The predictors of melanoma are progressive change in the shape, size and colour of moles. This guideline provides a series of photographs of moles, melanomas and other skin lesions, which may resemble melanomas.