BACKGROUND: Sarcoidosis is a multi-system disease of unknown etiology. Interferons (IFN) have been implicated in its pathogenesis. The objective of this study was to examine the causal relationship between sarcoidosis and IFN therapy. METHODS: Patients admitted for sarcoidosis (n=60) were reviewed for a history of IFN therapy. In addition, all cases of sarcoidosis in a cohort of hepatitis C-infected patients treated with IFN-alpha (n=1159) were analyzed. RESULTS: Five patients with prior IFN-alpha therapy and sarcoidosis were identified; an additional 23 have been reported in the literature. The median age of the 28 reported patients was 50 years, 16 (57%) were female, and 16 (57%) had isolated cutaneous disease. The median time to diagnosis was 4 months (range 1-16 months) following the introduction of IFN. A remission was observed in all patients with adequate follow-up (n=27): 15 (53%) upon dosage reduction or IFN discontinuation, seven (25%) with systemic corticosteroids, three (11%) with topical treatment, and three (11%) despite ongoing IFN therapy. Relapse was observed in both of the patients rechallenged with IFN. CONCLUSIONS: There is a potential causal relationship between IFN therapy and sarcoidosis. In patients with sarcoidosis in the setting of IFN therapy, the majority respond to IFN withdrawal or dosage reduction; however, some require corticosteroid therapy.