The aim of this study was to examine the cancer pattern in a large group of patients with rheumatoid arthritis (RA). A follow-up study of cancer incidence in RA was conducted within a cohort of 20,699 patients recorded in the Danish Hospital Discharge Register during 1977-1987 by linkage with the Danish Cancer Registry through 1991. There were consistent excesses of non-Hodgkin's lymphoma and Hodgkin's disease in both sexes and during both early and late periods of follow-up. Risks for lung cancer and non-melanoma skin cancer were also increased, with no predilection for any specific histological subtype, while risks for colorectal cancer and female breast cancer were reduced. The cancer pattern seen among Danish RA patients largely supports findings from two earlier Nordic investigations. Thus, there seem to be consistent positive associations between RA and non-Hodgkin's lymphoma, Hodgkin's disease and lung cancer and a consistent negative association with colorectal cancer.