The purpose of this article is to provide a clinical review of a unique, emerging form of severe social withdrawal that has been described in Japan. This paper begins with a case vignette, then reviews the case definition, epidemiology, psychopathology, differential diagnosis, and treatment and management of the condition. Called hikikomori, it is well known to both the psychiatric community and general public in Japan but it has never been reviewed in the English medical literature. Patients are mostly adolescent and young adult men who become recluses in their parents' homes for months or years. They withdraw from contact with family, rarely have friends, and do not attend school or hold a job. Never described before the late 1970s, hikikomori has become a silent epidemic with tens, perhaps hundreds, of thousands of cases now estimated in Japan. The differential diagnosis includes anxiety and personality disorders, but current nosology in the Diagnostic and Statistic Manual of Mental Disorders may not adequately capture the concept of hikikomori. Treatment strategies are varied and lack a solid evidence base, but often include milieu, family, and exposure therapy. Much further research, including population-based and prospective studies, needs to be conducted to characterize and provide an evidence base for treatment of this condition.