The transdiagnostic approach proposes the existence of common factors and processes underlying a wide range of mental disorders. This paper focuses on the relationship between narcissistic and avoidant personality disorders, as well as the role of vulnerable narcissism and impostor syndrome. Vulnerable narcissism and impostor syndrome share many similarities with these disorders, such as fear of criticism, and hypersensitivity to evaluation, which led to the hypothesis that they act as transdiagnostic factors. We also examined the role of these factors in psychological distress. The research included 309 participants. Psychodiagnostic instruments were used to assess the severity of narcissistic and avoidant personality disorders, vulnerable narcissism, and impostor syndrome. A questionnaire was used to assess current psychological distress and to measure sociodemographic variables. The results showed correlation between vulnerable narcissism, impostor syndrome, narcissistic personality disorder, and avoidant personality disorder. The hypothesis about vulnerable narcissism, and impostor syndrome acting as transdiagnostic factors was confirmed, although their role needs to be explored further in future research. In addition to both personality disorders, impostor syndrome independently and additionally contributed to current psychological distress. The results highlight the importance of treatment of impostor syndrome and the need for further research on the role of vulnerable narcissism in psychological distress.