Hikikomori is a severe form of social withdrawal increasing among the young Italian population. Hikikomori has been connected to psychological problems and high environmental sensitivity. Nevertheless, only a few studies have been carried out in the Italian context, and they did not analyze several aspects strictly related to the hikikomori phenomenon, such as the role of attachment and sensitivity. We aimed to investigate the relationship between attachment, sensitivity, and psychological problems in a sample of Italian hikikomori. Our sample comprised 72 Italian adolescents and young adults (49 males and 23 females), meanly aged 22.5 years, recruited through online forums and clinical centers for the hikikomori phenomenon. Our participants fulfilled the Highly Sensitive Person Scale (HSPS), the Attachment Style Questionnaire (ASQ), and the Hopkins Symptom Checklist (SCL-90-R). The results showed high psychological issues (i.e., depression and anxiety), environmental sensitivity, and insecure attachment orientations. Moreover, we discovered a significant relationship between attachment dimensions, environmental sensitivity, and psychopathology. Our study sheds light on a novel research path and could help both the researchers and the clinicians who work with people suffering from social withdrawal.