The authors report a case of a 49-year-old patient presenting with dysthyroid ophthalmopathy, who was treated with interferon alpha for chronic hepatitis C. Proptosis appeared 3 months after treatment onset and many complications occurred over more than 1 year. The extreme severity seen in this case is infrequent. After a summary of other ocular damage linked to interferon, the authors suggest that every interferon treatment include a check-up before beginning therapy and regular biological and ophthalmological monitoring.