There will be changes in the accounting regulations in Sweden. Firms will be categorised as K1-K4 firms depending on the size of the company. There will be different levels of accounting in the four categories. Firms will always have the possibility to choose a more advanced accounting regulation than the one they are obligated to due to their size. The purpose of this dissertation is to investigate which factors that influence the management in K3 firms in the choice between the K3 and K4 regulation. This dissertation has a deductive approach, and the theories that have been applied are the institutional theory and positive accounting theory. Based on these theories hypotheses have been developed. The study is based on a questionnaire survey- and on document studies. The respondents are 190 Swedish firms that will be categorised as K3 firms due to their size. The results of the study have been analysed and our findings showed that three of our hypotheses could not be discarded as factors that influence management in their choice of accounting regulation. The three factors are management compensation based on reported profits, size of the firms, and if the firms have parent companies listed on either Swedish or foreign stock markets.