The new perception of selective mutism as an anxiety disorder enables specialists to diagnose it early and take therapeutic measures as soon as possible. It is not an easy task to diagnose selective mutism and that process can engage many specialists. A diagnostic test should identify a pattern, depth and effects of selective mutism and also check whether there occur other serious problems related to this disorder. The test should help to determine how well do the people dealing with SM understand it and whether they apply the correct treatment. It should also help to collect full information on development, interests and friendships of a child to be able to help him efficiently. The aim of the article is to present the selective mutism and is to present the diagnosis as the process and to offer some suggestions how to classify the stages of this process.