The clinical relevance of the degree of severity in addiction disorders supports the need to investigate the variables underlying this aspect of the phenomenon. This study aimed to explore the relationships between factors that may influence the severity of addiction disorder, with a particular focus on temperamental disinhibition, emotion dysregulation, interpersonal vulnerability, and their interactions. A clinical sample of 502 (77% males and 22% females) was involved. All participants received a DSM-5 clinical diagnosis of "Substance-Related and Addictive Disorders" and were recruited from the Italian National Health System. The collected data were analyzed by implementing a chained mediation model using structural equation modeling. The statistical appropriateness of the hypothesized latent 4- factors model was confirmed. Specifically, temperamental disinhibition (composed of impulsiveness, compulsiveness, and obsessiveness), emotion dysregulation (composed of affect dysregulation, alexithymia, and dissociation), interpersonal vulnerability (composed of traumatic experiences, preoccupied, avoidant and unresolved attachment), and Addictive Disorders Severity (composed by substance use severity, alcohol use severity, gambling severity, and Internet use severity) were the four factors which have been identified. Furthermore, a total chained mediation model emerged, where emotion dysregulation and interpersonal vulnerability mediated the relationship between temperamental disinhibition and Addictive Disorders Severity. Our findings offer a better understanding of the variables associated with addictive disorder severity, providing important indications for therapeutic interventions.