Background: Patients diagnosed with a personality disorder (PD) are often stigmatized by the healthcare staff who treat them. Aims: This study aimed to compare the impact on front-line staff of a self-management Acceptance and Commitment Therapy-based training intervention (ACTr) with a knowledge- and skills-based Dialectical Behaviour Training intervention (DBTr). Method: A service-based randomized controlled trial was conducted comparing the effects of 2-day ACTr (N = 53) and DBTr (N = 47) staff workshops over 6 months. Primary outcome measures were staff attitudes towards patients and staff-patient relationships. Results: For both interventions, staff attitudes, therapeutic relationship, and social distancing all improved pre- to postintervention, and these changes were maintained at 6-month follow-up. Conclusions: Although offering different resources to staff, both ACTr and DBTr were associated with an improved disposition towards PD patients. Future research could evaluate a combined approach, both for staff working with PD patients and those working with other stigmatized groups.