A case of palsy without family history associated to hyperthyroidism, is described. This is an rare entity in our environment (only two cases have been previously described) and may develop with hypo, normo or hyperkalemia. Its potential pathogenicity is discussed, which finally results in a disorder of the ionic interchange at the level of the muscle membrane. The need to identify these secondary forms of recurrent palsy is stressed, given that it may benefit from an adequate treatment. In the case presented here, the normalization of the thyroid function was followed by the sustained elimination of the muscle symptomatology.