Solar keratoses (SKs) or actinic keratoses are common dysplastic epidermal lesions which occur in pale-skinned individuals who are chronically exposed to intense sunlight. Together with basal cell carcinomas and squamous cell carcinomas, they constitute a major public health problem in such individuals. Reported SK prevalence rates range from 11 to 25% in various northern hemisphere populations, and amongst Australian adults the range is from 40 to 60%. In the only study to date reporting SK incidence data, 60% of subjects aged 40 years and over with SKs at baseline developed new lesions during 12 months of follow-up, compared with only 19% of those who were lesion-free on the first examination. Because existing epidemiological data on SKs are sparse, very little is known of their natural history, their role in carcinogenesis, or their preventability. In this review, current knowledge about the aetiology, diagnosis, and occurrence of SKs is discussed, as is the need for prospective studies in unselected communities. With accurate baseline data, public health authorities should be in a better position to determine the best preventive strategies, and to evaluate the effectiveness of these programmes.