Monopoly represents the most extreme form of imperfect competition of market state, where one seller prevails and there is no equivalent substitute for his products. In imperfect competition, the dominant seller in such market structure can influence the price, to a certain extent, contrary to the perfect competition, where it's true that no company has the individual power to affect the price. If the monopolist wants to increase his sales, he has to lower the price because the demand curve in a monopoly is always downward sloping. The main reasons for the existence of monopolies are barriers that are preventing entry to such market, which make other potential challengers and competitors economically insufficient. UHCs form the tertiary level of health care in the Republic of Croatia. The largest expenditures in healthcare go exactly to the tertiary level, more precisely to the most complex organization, the UHC. Even if the number of healthcare providers grows, there is no competition in the segment of hospital treatment and other services offered by UHC. Although UHCs have a monopoly position, this does not mean that they operate without instability. Accumulated debts and poor management decisions from the past have left their mark on the operation of these complex systems, even to this day. In the first part, the paper will deal with the theoretical part of monopoly, more precisely the characteristics, structures, types and strategic management in monopoly. The second part will describe costs and their importance in managerial decision-making. And finally, in the third part, a detailed insight into the operations of UHC will be given, with an emphasis on the importance of costs, which greatly influence the decision-making of managers in UHCs.