Abstract: We identified incident cases of primary hepatocellular carcinoma (PHC) in the Northern Territory from 1980 to 1989: there were 18 Aboriginal and six non-Aboriginal cases, yielding incidence rates of 5.2 per 100 000 (Aboriginal) and 0.5 per 100 000 (non-Aboriginal) with a relative risk of 10.4 (95 per cent confidence interval (CI) 4.0 to 26.6). The carcinoma was more frequent in males (2.3 per 100 000) than in females (0.7 per 100 000), with a relative risk of 3.4 (CI 1.3 to 9.3). Incidence increased with age; the trend was statistically significant in Aborigines (X21, = 4.7, P < 0.05) but not in non-Aborigines (X21 = 3.4, P > 0.05). Hepatitis B virus (HBV) serology was available for 11 Aboriginal and four non-Aboriginal cases; seven of the Aboriginal cases and two of the non-Aboriginal cases were positive for hepatitis B surface antigen (HBsAg). The prevalence of HBsAg in Aboriginal patients with the carcinoma (63.6 per cent) was much higher than that (13.1 per cent) in Aborigines surveyed from communities in the Northern Territory (X21 = 21.7, P < 0.001). Our results show that the age-specific incidence of PHC in Aborigines in the Northern Territory (30.9 for ages 40 and over) is comparable to that in high-incidence countries such as China (36.9 for ages 40 and over), and that hepatitis B is of major aetiological importance in the Aboriginal population. This underlines the importance of universal immunisation for prevention of HBV infection and for long-term prevention of PHC.