A retrospective study was made of 858 cases of anal epidermoid carcinoma notified to the Swedish Cancer Registry in the 15-year period 1970-1984. The mean age at diagnosis was 67 years, with 5% (45) of the patients aged 25-44, 37% (314) aged 45-64 and 58% (499) greater than or equal to 65 years. All three age groups showed female predominance (c. 2:1), and the mean annual age-adjusted incidence/100,000 population was 1.40 for women and 0.68 for men. Incidence was highest in the cities of Stockholm (1.89) and Malmö (1.53). A strongly positive correlation was found between incidence of the disease and proportion of the population living in urban areas. Substantial annual rise (mean 4.3%) in incidence occurred during the study period, approximately the same in both sexes, in all age groups and in different "risk areas".