Little is known about the cancer risk following sarcoidosis. In a retrospective cohort study, we tested the hypothesis of an increased risk for malignant lymphomas, lung cancer as well as cancer in other organs frequently involved in sarcoidosis. Four hundred seventy-four patients from an incidence study 1966-1980 and 8,541 patients identified in the Swedish Inpatient Register (IPR) 1964-1994 were linked to the Cancer Register, the Register of Causes of Death, and the Register of Total Population. Relative risks were estimated using standardized incidence ratios (SIR). The overall relative risks for cancer were similar and elevated in both cohorts (IPR presented), SIR = 1.3; 95% confidence interval (CI) 1.2 to 1.4. For lung cancer and non-Hodgkin's lymphoma, the relative risk was doubled during the first decade of follow-up. Thereafter, the risk for lung cancer was significantly decreased whereas the risk for non-Hodgkin's lymphoma equaled unity. Throughout follow-up, elevated risks were found for melanoma (SIR = 1.6; 95% CI 1.0 to 2.3) and nonmelanoma skin cancer (SIR = 2.8; 95% CI 2.0 to 3.8). An increased risk was also found for liver cancer (SIR = 1.4; 95% CI 0.8 to 2.2). Thus, sarcoidosis appears to be associated with a significantly increased risk for cancer in affected organs. Chronic inflammation is a putative mediator of this risk.