Accounting standards are the rules and principles used in the preparation and presentation of financial statements. Their role is very important in assessing the success of the company. Every company must have a true and fair view of the financial statements according to accounting standards. This thesis analyzes the role of accounting standards in the evaluation of business performance of related companies, Vetropack Straža d.d. which is engaged in the production, distribution and sale of glass packaging and the company OMCO Croatia d.o.o. which is engaged in the production of tools for the manufacture of glass packaging. Both companies belong into the category of large enterprises and apply International Financial Reporting Standards. Therefore, emphasis is placed on the influence of accounting standards on the quality of reporting for users of financial statements. The aim of this thesis is to investigate the role of accounting standards in the financial reporting of these related companies and to evaluate their business based on financial statements and financial indicators. By vertical analysis of the balance sheet and profit and loss account, it was determined that the most significant accounting standards which regulate recognition and measurement in the observed companies are inventories (IAS 2), plant and equipment (IAS 16) and income (IFSI 15). Based on the analysis through financial indicators, the companies are liquid, indebtedness is low, they settle their accounts receivables and are profitable. It is concluded that accounting standards have a great influence and a significant role in the evaluation of business performance, they must provide a true and fair presentation of the basic financial statements and ensure an easier understanding and interpretation of the necessary data for all users.