The subject of this paper is to get acquainted with the institute of extreme necessity, in particular the types and legal effects. The goal of the paper is as close as possible explain theories about the existence of ultimate necessity, the notion of danger, the exceeding of extreme necessity, and the similarities and differences to the necessary defense. Ultimately it is necessary to eliminate the simultaneous danger which otherwise could not be removed, provided that the evil that occurred was lesser than the one that was threatened or disproportionately greater. The legal effect of an action taken in extreme urgency can be the exclusion of unlawfulness (when the evil that occurred is lesser than the one that threatened), or exclusion of guilt (when the evil that occurred is not disproportionately greater than the one that threatened). Croatian Criminal Law by adopting its differentiating theories follows the European standards and distinguishes the two types of extreme necessity. One of those is the reason for the exclusion of unlawfulness, and the other reason for the exclusion of guilt.The earlier criminal legislation also accepted differing theories, but with different content. With the utmost necessity as a reason for the exclusion of unlawfulness the law prescribes the ultimate necessity as a reason for (obligatory) exemption from punishment. Divisions that have to be fulfilled to be of ultimate concern can be divided into three groups: the first group refers to the state of danger, the second is related to the action that removes the danger, and the third relates to the relationship between the evil and the threatened.