The data used for the inter-Nordic comparison of the incidence of skin cancer are based on the material of the national cancer registries of the 5 Nordic countries. It is typical of these countries that the ratio between the incidence of non-melanoma and melanoma skin cancer is much smaller than in regions near the Equator. For the detailed comparative epidemiological study of basal-cell carcinoma (BCC), squamous-cell carcinoma (SCC) and cutaneous malignant melanoma (CMM), the material from the Norwegian Cancer Registry 1955-1988 is used. The etiology of CMM has frequently been debated during recent decades. There are still some obscure points, however, particularly as regards the influence of host factors and UV exposure, and their interaction. The analysis of the incidence trend of CMM on the female breast during the time interval 1970-1988 contributes to the elucidation of these problems. Differences in the epidemiological characteristics of the 2 main types of non-melanoma skin cancer, BCC and SCC, are described. The results indicate that the effect of UV light is not a dominating for BCC as for SCC.