Resistance syndrome to thyroid hormone (RTH) is a rare autosomal dominant disease that is characterized by decreased tissue responsiveness to thyroid hormone, and it is mainly due to mutations of the thyroid hormone receptor beta (THRB) gene. We report here on a 36-years old male who had mild thyroid goiter and general weakness. The thyroid function test showed elevated levels of total T3 and free T4. The levels of TSH and the free alpha subunit were in normal ranges. Mutation analysis of the THRB gene revealed the missense mutation G345D. We report here on the clinical features and THRB gene mutation analysis of a case of RTH.