We present a case of familial disease, focal acral hyperkeratosis (FAH), associated with hyperthyroidism that subsequently turned into thiamazole-induced hypothyroidism. To our knowledge, there have been no reports that describe the association between FAH and hyperthyroidism. FAH is a rare type of marginal papular keratoderma and its etiology is still unknown. In the present case, we observed that thiamazoleinduced secondary hypothyroidism was accompanied by a rapid increase of skin lesions. Therefore, we speculate that there is a causal relationship between the deterioration of FAH and the altered thyroid function by the usage of thiamazole.