Separation Anxiety Disorder has been recently classified into the DSM-5 section of Anxiety Disorders, acknowledging its role not only in childhood and adolescence but also across the whole lifespan. In the DSM-IV-TR, in fact, this condition was typically considered to begin in childhood. Clinical data report prevalence rates from 20 to 40%, showing high comorbidity rates with most mental disorders. Epidemiological data highlight that in fact one third of childhood cases persist into adulthood, while the majority of adult cases reports its first onset in adulthood. In all cases, Separation Anxiety Disorder is associated with a severe impact on the overall functioning. Most relevant research in the field is discussed highlighting the need of a paradigm shift in which clinicians are alerted to identify and treat this condition in all age upon the recent DSM-5 reformulation will be highlighted.