Introduction: Since the 1990s the term “Hikikomori” has emerged as a way to describe a modern form of severe social withdrawal first described in Japan. Recently, there have been increasing reports of Hikikomori around the globe.Objectives: To describe operationalized research criteria for Hikikomori, as well as epidemiologic, diagnostic, and psychosocial features of the Hikikomori in international settings.Methods: Participants were recruited from sites in India, Japan, Korea, and the US. Hikikomori was defined as a six-month or longer period of spending almost all time at home and avoiding social situations and social relationships, associated with significant distress/impairment. Lifetime history of psychiatric diagnosis was determined by the Structured Clinical Interview for the DSM-IV Axis-I and Axis-II Disorders. Additional measures included the Internet Addiction Test, UCLA Loneliness Scale, Lubben Social Network Scale (LSNS-6), and Sheehan Disability Scale (SDS).Results: Thirty-six participants meeting diagnostic criteria for Hikikomori were identified, with cases detected in all four countries. Avoidant personality disorder (41%), major depressive disorder (32%), paranoid personality disorder (32%), social anxiety disorder (27%), posttraumatic stress disorder (27%), and depressive personality disorder (27%) were the most common diagnoses. Sixty-eight percent had at least two psychiatric diagnoses. Individuals with Hikikomori had high levels of loneliness (UCLA Loneliness Scale M = 55.4, SD = 10.5), limited social networks (LSNS-6 M = 9.7, SD = 5.5), and moderate functional impairment (SDS M = 16.5, SD = 7.9).Conclusions: Hikikomori exists cross-nationally and can be assessed with a standardized assessment tool. Individuals with Hikikomori have substantial psychosocial impairment and disability, and a history of multiple psychiatric disorders is common.Disclosure of interest: The author has not supplied his declaration of competing interest.