Five-year survival rates were slightly higher for patients with cutaneous malignant melanoma (CMM) diagnosed in Western Australia in 1980/1981 (89% in men and 95% in women) than in those whose melanomas were diagnosed in 1975/1976 (88% in men and 91% in women). The improvement in survival was probably due to a decrease in median tumor thickness from 1.29 mm in 1975/1976 to 0.77 mm in 1980/1981 because tumor thickness was the most important histologic index of prognosis. Tumor cell type and cross-sectional profile were the only other histologic characteristics that independently influenced fatality rates. Prognosis was significantly worse in males than in females and in patients with tumors on the posterior head and neck. Ten-year survival rates of patients whose melanomas were diagnosed in 1975/1976 was 82% in men and 87% in women, indicating that these patients continued to experience some excess mortality up to 10 years after diagnosis. The comparatively small improvement in prognosis in the 5-year period between these two groups suggests that survival might be expected to continue to improve only gradually unless there is a sharp absolute decrease in the number of thick tumors diagnosed.