Purpose. The aim of this study was to determine the antifibrotic effects of pirfenidone in orbital fibroblasts of patients with thyroid-associated ophthalmopathy (TAO). Methods. The effects of interleukin (IL)-1j3 and of fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), and transforming growth factor (TGF)-j3 on the induction of tissue inhibitors of metalloproteinases (TIMP)-1 were assessed in orbital fibroblasts of TAO patients. TIMP-1 protein levels were measured by ELISA and Western blot analyses, and TIMP-1 activity was assessed by reverse zymography. The effect of pirfenidone on TIMP-1 induction in orbital fibroblasts was evaluated with the same methods using dexamethasone as a reference agent. A hydroxyproline assay was used to determine the effect of pirfenidone and dexamethasone on collagen production in orbital fibroblasts, and the tetrazolium-based MTT assay was used to assess pirfenidone cytotoxicity. Results. IL-1j3 strongly and dose dependently increased the level of active TIMP-1 protein, whereas FGF, PDGF, and TGF-/3 did not significantly induce TIMP-1 protein. Pirfenidone was more effective than dexamethasone in inhibiting IL-1j3-induced increases in TIMP-1, reducing TIMP-1 levels to less than those in untreated controls at a minimal concentration (5 mM). Moreover, pirfenidone effectively decreased hydroxyproline levels in orbital fibroblasts, whereas dexamethasone had no effect on hydroxyproline levels. Pirfenidone exhibited no toxicity in orbital fibroblasts at the concentrations used. Conclusions. These results indicate that nontoxic concentrations of pirfenidone have significant antifibrotic effects on orbital fibroblasts from patients with TAO.