A cohort of 412 patients first attending a cystic fibrosis (CF) clinic between 1961 and 1989 were followed up to 30 June 1989. The number of malignancies observed in the cohort was compared with the number expected based on the age, sex and calendar-year-specific cancer registration rates for England and Wales. Four CF patients were diagnosed as having malignancies before 30 June 1989. The tumours were: adenocarcinoma of the terminal ileum; adenocarcinoma of the pancreas, testicular teratoma, and B-cell lymphoma. This compares with 0.89 malignancies expected on the basis of rates in England and Wales (Standardised Registration Ratio = 452; 95% confidence interval 122-1150, P = 0.03). The single case of adenocarcinoma of the terminal ileum contrasts with less than 0.001 expected (P = 0.003) and that of the pancreas with 0.007 expected (P = 0.01). A further adenocarcinoma of the pancreas was diagnosed 2 years after the end of the study period. The two cases of pancreatic cancer compare with 0.008 expected (P = 0.0001) during the period to mid 1991. On the basis of the present findings and previous case reports in the literature adenocarcinoma of the pancreas and adenocarcinoma of the terminal ileum may be associated with cystic fibrosis.