The Companies Act does not define the shareholders' meeting, but according to the literature, it is a body of the joint stock company through which shareholders of a joint stock company express their will and exercise rights and it must be held once a year. Decisions made at the shareholders' meeting can be positive or negative, depending on the outcome of the voting. With regard to substantive and formal legal rules, we distinguish following types of the shareholders' meeting decisions with deficiency: ostensible decisions, decisions without legal effect, void decisions and voidable decisions.. In the case of an ostensible decision, it appears to exist but does not actually exist. A decision without the legal effect is a decision that was validly made at the shareholders' meeting, but for its legal effect the fulfillment of additional assumptions is also required. A void decision is one that contains a serious legal defect, due to which the legal order does not recognize it. A voidable decision is one that contains a legal defect, but is not legally void until someone successfully challenges it. The Companies Act regulates the procedure for determining the nullity and rebbuting the decisions of the shareholders' meeting. It determines reasons for invalidity, legal remedies and entities that can use them against invalid decisions and legal consequences of invalidity.