Clinical and pathologic characteristics of melanoma were compared among 1647 clinical Stage I patients treated at the University of Alabama in Birmingham (USA) and The University of Sydney (Australia) between 1955 and 1980 to determine what changes occurred over a quarter century. Over this period, the number of patients treated annually has increased substantially. There was a steady increase in the proportion of patients presenting with localized disease (clinical Stage I). Melanomas became thinner, less invasive, less ulcerative and thus more curable. They also exhibited more of a radial growth phase. The median thickness of melanomas decreased in Australia from 2.5 mm prior to 1960 to 1.1 mm during the period 1976 to 1980, while in Alabama it has decreased from 3.3 to 1.4 mm. There was a significant increase in melanomas located on the trunk in males and a corresponding decrease in male head and neck melanomas. No significant change in the site distribution was observed for any major anatomical area on female patients. There were minimal differences in the incidence of both clinical and pathologic parameters among melanoma patients in Alabama, USA and in New South Wales, Australia even when accounting for their year of diagnosis. Long-term survival rates in patients with localized disease were found to increase slightly during the 25 year time frame of this analysis. The changes that have occurred are likely due to earlier diagnosis and changes in the biological nature of the disease.