This thesis deals with the issue of internal audit. The aim of the thesis is to evaluate the need for internal audit in the conditions of the selected company by applying the theoretical knowledge and to propose an audit plan. The theoretical part introduces the development of the auditing profession, important institutes associating internal auditors and professional requirements. Among other things, there is also clarified a relationship between external and internal audit. An important chapter is a description of the entire process of the internal audit including proper documentation. After a detailed presentation of the company PETROF, spol. s r.o. at the beginning of the practical part, reflection is made on the use of internal audit. ...