Xeroderma pigmentosum (XP) is a rare hereditary disease characterized by a very high frequency of skin tumours due to a defect in the nucleotide-excision-repair process. Some of these patients have also been reported to develop internal tumours with higher frequency than the normal population. Reported here are the clinical features and molecular analysis of an XP patient who developed multiple skin cancers as well as a thalamic glioma. Complementation analysis with recombinant retrovirus, cloning efficiency and unscheduled DNA synthesis after UV-C indicate that the patient belongs to the C group. Characterization of the p53 mutations in the 2 tumours of the patient leads to speculation on the aetiological agents involved in tumour initiation. The skin tumour is clearly induced by the presence of unrepaired UVB-induced DNA damage on the non-transcribed strand of the p53 gene, while the glioma may be induced by unrepaired DNA lesions produced by free radicals.