We report the case of a caucasian woman who, between the ages of 49 and 51 years, developed multiple (> 20) basal cell carcinomas (BCC). There was no family history of BCC. No abnormalities in the human homologue of the Drosophila segment polarity gene patched (PTCH), glutathione S-transferases T1 and M1, or cytochrome P450 1A1 were detected by polymerase chain reaction (PCR)-based molecular analysis. There was, however, actinic damage of the skin in sun-exposed areas. The patient was diagnosed as having hairy cell leukaemia (HCL) at the age of 51 years, based upon leucocyte morphology as assessed by light and electron microscopy, tartrate-resistant acid leucocyte phosphatase (TRAP) staining, fluorescence activated cell scanning of peripheral blood leucocytes and bone marrow histology. As the leukaemia slowly progressed over a 3-month period, the patient developed four further BCCs. Given that HCL is characterized by a profound defect in T-cell function, it is conceivable that T-cell immune dysregulation can contribute to the pathogenesis of BCC, possibly enhancing the aetiological effect of ultraviolet irradiation.