The article presents the classification of imperfections present in joints welded using the FSW method. The division of imperfections is based on standards PN-EN ISO 25239:2013 and AWS D17.3. The article also provides a more extensive and precise division of welding imperfections characteristic of the FSW process along with reasons for their formation. The text also presents the requirements of the standards in relation to the boundary values of imperfections depending on imperfection types. Furthermore, the article demonstrates the advantages, disadvantages and application of given non-destructive tests with reference to the quality control of FSW joints.