Eight cases of sarcoidosis diagnosed after a preceding malignant solid tumor are presented. An analysis of these eight cases along with four previously reported cases was unable to answer the question whether in some cases the development of sarcoidosis may be triggered or modified by a preceding treatment of a malignant tumor. However, in the reverse situation--sarcoidosis preceding cancer--an analysis of 23 such cases from the literature suggests that sarcoidosis preceding cancer appears to be of the chronic active variety and that lung and breast cancer may occur more often than expected after sarcoidosis. Thus, it is conceivable that the immunologic abnormalities associated with sarcoidosis may somehow promote the development of certain malignant tumors. True sarcoidosis may be confused with local sarcoid reactions in cancer patients. One such case is reported in which the finding of a regional sarcoid reaction to a solitary lung metastasis from a uterine adenocarcinoma led to insufficient treatment in the belief that the patient had systemic sarcoidosis.