The position of selective mutism disorder – SM – has been modified in the last edition of the classification of mental disorders DSM-5. It was removed from “Disorders of childhood and adolescence” and placed in “Anxiety disorders”. This caused two important changes in the interpretation of the symptoms of selective mutism. It highlighted anxious etiology of the disorder and also open the possibility to diagnose selective mutism in adults as a special category of anxiety disorders. The aim of this study was to present three different cases concerning the diagnostic difficulties of selective mutism (the child, the teenager and the persons who became adult during our observation) regarding current views on SM. In this study we presented the current view on the etiology, course and available therapies for selective mutism. Owing to updating the clinical knowledge about SM and describing three cases, we highlighted the controversies around the diagnosis and treatment of this disorder. Selective mutism might be a preliminary diagnosis, often leading to the diagnosis of other disorders of diverse etiology and course. Among the psychiatric aspects of the disorder, the ‘anxiety component’ of SM is crucial. In individuals with selective mutism, developmental disorders, social cognition and neurocognition deficits or dysfunctions of auditory processing often coexist. The severity and the type of comorbidities may determine the future course of the illness and the final effects of the therapy.