Thymus cancer epidemiology has been little investigated, but recent clinical studies have suggested an association with the Epstein-Barr virus. We studied thymus cancer incidence 1963-83 and mortality 1959-86 in England and Wales, using data from the National Cancer Register and national mortality files. Mean age-standardised incidence rates of the tumour were 0.72 per million per annum for males and 0.64 for females; mortality rates were about half of this: 0.43 for males and 0.29 for females. There was no significant change in rates over time, nor any consistent pattern of risk by region of residence. Birth cohort analysis of mortality showed in each sex, lowest risk for persons born during the Second World War. The age distribution of the tumour was unusual: a progressive rise in both incidence and mortality rates occurred in each sex at ages up to 60-69, at which there was a striking peak, more marked for males and for incidence data, with a sharp decline thereafter. Immigrants from China and Cyprus had significantly high proportional registration ratios, but based on small numbers.