The structure of integrated hepatitis B virus (HBV) DNA was analysed to determine the origin of recurrent and multinodular hepatocellular carcinoma (HCC). In 5 cases, recurrent tumours were compared with the respective primary tumours, all of which had chromosomally integrated viral DNA. In only one of these cases, an identical HBV DNA integration pattern was found, indicating a monocentric origin of primary and secondary tumour. In all other cases a polycentric origin was deduced. Particular features observed were: (i) the apparent absence of integrated viral DNA in a recurrent tumour; and (ii) an integration pattern identical to that of the primary tumour and a distinct new pattern in two different foci of multinodular recurrent HCC. For multinodular primary HCC one case was analysed and found to be of independent origin.