The article describes the process of planning internal audits carried out in the framework of a quality management system based on ISO 9001. The article presents some errors made in the planning process of internal audits. These errors are classified as potential causes of poor effectiveness audits. In the first part this article contains theoretical considerations in the planning of internal audits of quality management systems. The second part of the article presents the results of research. These results illustrate the effects of errors in the planning process of the audit. At the end recommendations for persons responsible for planning audits are included. These recommendations should improve the effectiveness of the internal audit planning, and thereby their value to the organization