In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) separation anxiety disorder has been included in the chapter on anxiety disorders, thereby removing the age of onset restriction that previously required first onset during childhood or adolescence. Separation anxiety disorder has a lifetime prevalence of 4.8% and onset often occurs after the age of 18 years. Despite the high prevalence, separation anxiety disorder is often underdiagnosed and subsequently remains untreated. This narrative review summarizes the etiology, clinical features, diagnostic criteria as well as important differential diagnostic aspects, common comorbidity profiles and treatment implications of separation anxiety disorder. Furthermore, relevant implications for everyday practice and future perspectives for treatment and research are discussed.