During the mid to late 1980s in white populations in Australia, New Zealand, and Scotland, melanoma incidence increased sharply above preceding long-term trends. Most of this increase was in thin melanomas (< 1.50 mm thick), and men were more affected than women. Thick melanomas also generally increased in incidence, particularly in men 65 years or older. Although advancement of the time of diagnosis was a likely factor in the increase in melanoma incidence, the maintenance of new higher incidence levels and the increase in the incidence of thick lesions indicated that earlier diagnosis did not explain most of the increase. Real increases in incidence due to continuation of long-term trends and the increasing diagnosis of a preexisting, nonmetastasizing form of thin melanoma probably explain most of the recent increases in melanoma incidence.