In the late 1990s, a severe and prolonged form of social withdrawal typically observed among adolescents and youth transitioning to adulthood entered the collective national consciousness in Japan. Called “hikikomori” , it has shifted in recent years from being viewed as a typical Japanese problem to an issue that may have global health implications1. This shift has been driven by increasing evidence of hikikomori in epidemiologic studies, clinical case series and media reports from around the world2.

As attention to hikikomori grows across cultures and countries, so does the importance of establishing a clear and consistent definition of the disorder. About a decade ago, preliminary diagnostic criteria3 and a semi‐structured diagnostic interview4 were developed. Over the last decade, we and others in this emerging field of research have gained a wider breadth of experience in evaluating, treating and following up a series of individuals with hikikomori, as well as their family members, in Japan and beyond. This has led to an evolution in our biopsychosocial understanding of the disorder4, 5, and an acute awareness of the limitations of its earlier definitions. We believe it is time now to provide an updated proposal of diagnostic criteria for hikikomori, which is presented here.

Hikikomori is a form of pathological social withdrawal or social isolation whose essential feature is physical isolation in one's home. The person must meet the following criteria: a) marked social isolation in one's home; b) duration of continuous social isolation of at least 6 months; c) significant functional impairment or distress associated with the social isolation.

Individuals who occasionally leave their home (2‐3 days/week), rarely leave their home (1 day/week or less), or rarely leave a single room may be characterized as mild, moderate or severe, respectively. Individuals who leave their home frequently (4 or more days/week), by definition, do not meet criteria for hikikomori. The estimated continuous duration of social withdrawal should be noted. Individuals with a duration of at least 3 (but not 6) months of social isolation should be classified as pre‐hikikomori. The age at onset is typically during adolescence or early adulthood. However, onset after the third decade of life is not rare, and homemakers and elderly who meet the above criteria can also receive the diagnosis.

Four aspects of this revised definition of hikikomori bear emphasis. First, the behavior of staying confined to home – the physical aspect of withdrawing and remaining socially isolated – remains hikikomori's central and defining feature. However, the definition adds clarification as to what frequency of going outside home still qualifies as “marked social isolation in one's home” . Second, the requirement for avoidance of social situations and relationships has been removed. In our interviews assessing individuals for hikikomori5, they commonly report having few meaningful social relationships and little social interaction, but deny avoiding social interaction. Many clinicians often wonder about what distinguishes hikikomori from social anxiety disorder, and this lack of avoidance is one of the primary differences.

Third, distress or functional impairment should be carefully evaluated. While impairment in the individual's functioning is vital to hikikomori being a pathological condition, subjective distress may not be present. Our in‐depth clinical interviews with people with hikikomori4 have revealed that many actually feel content in their social withdrawal, particularly in the earlier phase of the condition. Patients frequently describe a sense of relief at being able to escape from the painful realities of life outside the boundaries of their home. However, as the duration of social withdrawal gets longer, most people with hikikomori begin endorsing distress, such as feelings of loneliness4.

Fourth, we have removed other psychiatric disorders as an exclusion criterion for hikikomori. It is clear that this disorder tends to co‐occur with other conditions6, 7. In our view, the frequency of co‐occurring conditions increases the importance of addressing social withdrawal as a health issue. It is possible that hikikomori (pathological social withdrawal) co‐occurs with a variety of psychiatric disorders as a contributor to psychopathology, similarly to how catatonia and panic attacks are now listed as specifiers to several mental disorder diagnoses.

With advances in digital and communication technologies that provide alternatives to in‐person social interaction, hikikomori may become an increasingly relevant concern. We hope that these simplified diagnostic criteria may help standardize evaluation and encourage cross‐cultural comparison of hikikomori.