BACKGROUND: Recent developments have highlighted the importance of separation anxiety across the lifespan, positioning it as a longitudinal psychopathological dimension. Few studies in the past decade, have explored this correlation within the context of other psychiatric disorders. This study aims to assess the presence of childhood and adulthood separation anxiety in a sample of adults with personality disorders, and its potential contribution to specific personality domains. METHODS: A sample of 102 patients (39% male, 61% female) with a principal diagnosis of "Unspecified Personality Disorders" according to the Diagnostic and Statistical Manual of Mental Disorders - 5° edition - text revision (DSM-5-TR) was recruited. The patients were assessed using the following instruments: the Structured Clinical Interview for Separation Anxiety Symptoms and the Personality Inventory for DSM-5-Brief Form (PID-5-BF). Correlation and linear regression analyses were performed. RESULTS: Both childhood and adulthood separation anxiety were positively correlated with all PID-5 domains except "Antagonism" (p = 0.352/0.067). The linear regression analysis showed that only adult separation anxiety was a direct predictor of the personality domains "Negative Affectivity" (p = 0.002), "Detachment" (p = 0.008), and "Psychoticism" (p = 0.028). CONCLUSIONS: Our study is the first to highlight the potentially crucial role of adult separation anxiety levels in personality disorders. Unexpectedly, childhood separation anxiety did not predict personality domains. The presence of separation anxiety should be considered a potential developmental obstacle to a healthy transition toward a well-rounded adult personality organization.