Abstract The problem of ‘social withdrawal’ among young adults is the focus of considerable attention in Japan today. Among the various manifestations of social withdrawal, a ‘primary social withdrawal’ group has been identified that cannot be diagnosed by the established classification of mental disorders. In an earlier report it was suggested that the onset mechanism for primary social withdrawal is not merely a problem of the withdrawn person themselves, but also includes problems of family relationships. The aim of the present study was to identify the characteristics and problems in family relationships associated with primary social withdrawal. For that purpose a survey was conducted using David H. Olson's Family Adaptability and Cohesion Evaluation Scale as well as a questionnaire that the present authors devised on family interactions and the personal situation of the withdrawn person. The results pointed to the following four characteristics of primary social withdrawal families: (i) there are definite rules within the family; (ii) the families share values and an unfounded pride; (iii) there is a lack of emotional exchange in the family, and it is difficult for members to sympathize with each other's negative feelings; and (iv) although concerned about each other, there is little verbal exchange. From these family characteristics, the onset mechanism for withdrawal is triggered by insignificant matters such as minor setbacks in the developmental issues of youth. Then, given the person's personality traits and aforementioned characteristics in family relationships, the person becomes mired in social withdrawal.