AIM:To study predictive factors of thyroid dysfunction associated with interferon-alpha(IFNα) therapy in chronic hepatitis C(CHC) and to describe its long-term evolution in a large population without previous thyroid dysfunction.METHODS:We performed a follow-up of thyroid function and detection of thyroid antibodies in 301 patients treated for CHC with IFNα from 1999 to 2004.RESULTS:Thyroid disorder developed in 30/301(10%) patients with a mean delay of 6 ± 3.75 mo:13 patients had hyperthyroidism,11 had hypothyroidism,and 6 had biphasic evolution.During a mean follow-up of 41.59 ± 15.39 mo,9 patients with hyperthyroidism,3 with hypothyroidism,and 4 with biphasic evolution normalized thyroid function in 7.88 ± 5.46 mo.Recovery rate of dysthyroidism was not modified by treatment discontinuation,but was better for patients with negative thyroid antibodies before antiviral treatment(P = 0.02).Women had signif icantly more dysthyroidism(P = 0.05).Positive thyroid peroxidase and thyroglobulin antibodies were more frequent before antiviral treatment in patients who developed dysthyroidism(P < 0.0003 and P = 0.0003,respectively).In a multivariate model,low fibrosis was found to be a predictive factor of dysthyroidism(P = 0.039).CONCLUSION:In this monocentric population of CHC,dysthyroidism,especially hyperthyroidism,developed in 10% of patients.Low fibrosis was found to be a predictive factor of dysthyroidism.Thyroid disorder recovered in 16/30 patients(53%) and recovery was better in the non-autoimmune form. AIM: To study predictive factors of thyroid dysfunction associated with interferon-alpha (IFNα) therapy in chronic hepatitis C (CHC) and to describe its long-term evolution in a large population without previous thyroid dysfunction. METHODS: We performed a follow-up of thyroid function and detection of thyroid antibodies in 301 patients treated for CHC with IFNα from 1999 to 2004.RESULTS: Thyroid disorder developed 30/301 (10%) patients with a mean delay of 6 ± 3.75 mo: 13 patients had hyperthyroidism, 11 had hypothyroidism, and 6 had biphasic evolution. During a mean follow-up of 41.59 ± 15.39 mo, 9 patients with hyperthyroidism, 3 with hypothyroidism, and 4 with biphasic evolution normalized thyroid function in 7.88 ± 5.46 mo. Recovery rate of dysthyroidism was not modified by treatment discontinuation, but was better for patients with negative thyroid antibodies before antiviral treatment (P = 0.02) .Women had signif icantly more dysthyroidism (P = 0.05) .Positive thyroid peroxidase and thyrogl obulin antibodies were more frequent before antiviral treatment in patients who developed dysthyroidism (P <0.0003 and P = 0.0003, respectively) .In a multivariate model, low fibrosis was found to be a predictive factor of dysthyroidism (P = 0.039) .CONCLUSION: In this monocentric population of CHC, dysthyroidism, especially hyperthyroidism, developed in 10% of patients. Low fibrosis was found to be a predictive factor of dysthyroidism. Hyroid disorder recovered in 16/30 patients (53%) and recovery was better in the non- autoimmune form.