Objectives: We sought to test the Biosocial Theory of borderline personality disorder (BPD) that posits that borderline traits are due to emotional dysregulation, caused by the interaction between childhood emotional vulnerability and invaliding parenting. Method: A total of 250 adults (76% female, median age = 32.06 years) from a nonclinical population completed self-report measures assessing current levels of borderline traits and emotional dysregulation. They also completed retrospective measures of childhood emotional vulnerability and parental invalidation. Results: Invalidating parenting and emotional vulnerability independently predicted emotion dysregulation, but an interaction effect was not found. Having experienced validating parenting was found to be a protective factor for developing borderline traits but was not significantly related to emotional dysregulation. Conclusion: Data in this sample did not support the underlying genesis of BPD proposed by the Biosocial Theory and a model that more parsimoniously explains the development of BPD is proposed.