This paper discusses juridical and deontological problems that doctors has to deal with when a validly opposed refusal of a blood transfusion by a Jehovah's Witness endangers his own life. Decided that there is not any duty of a therapeutical intervention on the grounds of art. 328 and 359 of the italian penal code, it is critically examined the soundness of the systematically suggested recourse to the art. 54 of the italian penal code that offend against the inviolable rights of the human person as recognized and guaranteed by the Constitution of the italian Republic. The refusal of a blood transfusion by Jehovah's Witnesses it is part of the right to self-determination towards therapy and of that of freely professing one's own religious faith.