We describe a 34-year-old female treated with IFN-beta for 8 years with a biochemical profile suggestive of acromegaly. The patient presented with elevated serum insulin-like growth factor-I (IGF-I) and insufficient suppression of growth hormone (GH) during oral glucose tolerance test (OGTT). There were no clinical features of acromegaly. A 5-day profile showed higher GH levels on the 3 days following IFN-beta injections. Total and bioactive IGF-I were also elevated but did not fluctuate. Four weeks off IFN-beta normalized suppression of GH during OGTT but did not reduce serum IGF-I or bioactive IGF-I. In conclusion, IFN-beta treatment mimicked acromegaly biochemically. The changes were partially reversible