The number of certified companies was growing and according to the data of ISO Survey of ISO 9000 and ISO 14001 certification, 12th Cycle, 2002 at the end of 2002 there were more than 560 000 certificates issued totally. The most important clause of ISO 9001:2000, related to analysis, measurement and improvements, is requirement about internal audit. Internal audit is a process, which managed adequately, could give valuable information about company’s QMS and it’s effectiveness. However effectiveness and efficiency of internal audit differs from company to company and it has specific features in small and medium sized companies.