A population-based cohort of 37,674 patients diagnosed during the period 1978-1991 and registered in the Danish Cancer Registry with basal cell carcinoma of the skin (BCC) were followed for the occurrence of new malignancies. BCC patients experienced significantly increased cancer incidence rates compared with the general Danish population. The elevated cancer risk was not restricted to new cutaneous malignancies. Cancers at various sites, including lip, salivary glands, larynx, lung, breast, kidney and non-Hodgkin lymphoma occurred in significant excess. Patients diagnosed with BCC before the age of 60 years were at higher risk of developing new malignancies than patients diagnosed with BCC at an older age. This age association pertained particularly to breast cancer, testicular cancer and non-Hodgkin lymphoma.