BACKGROUND Studies have suggested that the incidence of classic Kaposi's sarcoma (KS) varies considerably within Europe. The epidemiology of classic KS in Denmark was described for the period between 1970 and 1992 and association with marital status and country of origin were evaluated. METHODS A descriptive epidemiology study was carried out using data from the Danish Cancer Registry and from all Danish pathology departments. The effects of marital status and of immigration were evaluated in a case-control study with sex- and age-matched controls for 50 cases of classic KS. RESULTS A total of 59 patients with classic KS, 34 men, 25 women, were identified between 1970 and 1992, yielding world standardized incidence rates of 0.40 and 0.22 per 1,000,000 population among men and women, respectively. Among men, a larger proportion of the patients with classic KS were of non-Danish origin [odds ratio (OR) = 3.8, 95% confidence interval (CI) = 1.5-9.6]. No excess of foreign born persons was observed among women with KS. Never-married men were at a markedly increased risk for classic KS (OR = 2.8, 95% CI = 1.2-6.7). This risk was, however, restricted to men younger than 60 years (OR = 18.8, 95% CI 3.4-104.8), whereas no increased risk was observed in men age 60 years or older nor was there an increased risk in women. CONCLUSIONS Classic KS is a rare disease in Denmark. However, men, immigrants and never-married men age 60 years or younger experienced an excess risk. Even though the latter finding might reflect an association with male homosexuality, the observation should be interpreted with caution due to the limited number of observations.