The age-standardized proportion of persons with solar keratoses in 1232 Australian-born persons who were aged 40 years and older was 44.5% compared with a proportion of 15.7% in 1332 British persons who had migrated to Australia at various ages. Stratification of the British migrants into those who had arrived in Australia between one and 20 years of age and those who had arrived in Australia after the age of 20 years revealed that the proportion of persons with solar keratoses in the latter group never reached the proportion in Australian-born persons of the same age, in spite of many years in Australia after migration. Those persons who arrived in Australia between one and 20 years of age showed a lower proportion with solar keratoses in the younger age-groups, but with increasing age the proportion with solar keratoses equalled or exceeded that which was seen in Australians. These results suggest that a reduction in exposure to sunlight in childhood will reduce substantially the incidence of solar keratoses, and by implication, squamous-cell carcinomas, in adulthood.