This article explores accruing evidence supporting the occurrence of an adult form of separation anxiety disorder (ASAD), a category yet to be recognized by international classification systems. ASAD can have its first onset in adulthood, although in a portion of cases, it represents a persistence or recurrence of the childhood-onset type. Recent large-scale clinic studies have suggested that ASAD is associated with high levels of disability. In addition, the presence of ASAD in individuals with anxiety disorders seems to signal a poor outcome to cognitive-behavioral therapy. The existing evidence suggests possible grounds for removing the childhood-onset requirement for the category of separation anxiety disorder, thereby allowing for first onset in adulthood. There is a pressing need to design and test appropriate treatments for ASAD and to educate clinicians to identify and manage the condition.