Death rates from colorectal cancer in Northern Ireland are higher than in most of the rest of the United Kingdom. Although local surgeons have recognised this problem for some time it has remained unclear whether this reflects a greater underlying incidence or a worse mortality. We have reviewed all histological diagnoses of colorectal cancer in the province over a three year period and we report the incidence and site distribution for this disease in this population of one and a half million. With the exception of rectal cancer in females the incidence of colorectal cancer, whether histologically diagnosed or registered, is higher than in England, Wales or Scotland. The site distribution accords with that in other high risk countries. These results indicate that Northern Ireland has the highest underlying incidence of colorectal cancer in the United Kingdom.