Melanomas are cancers arising from the pigment cells of the skin, and are among the most commonly occurring cancers in this country. Each year, more than 8,000 Australians are diagnosed with invasive melanoma, resulting in some 900 deaths annually. Sunlight is the principal factor which causes this disease, although there is increasing evidence that the role of sunlight in causing melanoma is not the same for all people who develop this disease. A new hypothesis proposes that the malignant course of melanomas may reflect their causal origins, with melanomas induced by chronic sunlight exposure perhaps being more aggressive than other melanomas. We will undertake a large study of patients with melanoma to investigate both the causal pathways and their influence on markers of tumour aggressiveness. We will capture detailed information about the microscopic appearance of the melanomas from pathologists at the time of diagnosis, and marry this to the information reported by the patients about their past history of sun exposure. When complete, this study will provide new information about the causes of melanoma. Such knowledge is crucial to controlling and preventing this cancer.