Dialectical behavior therapy (DBT) has become a widely used treatment model for individuals with borderline personality disorder (BPD) and other individuals with significant emotion dysregulation problems. Despite its strong empirical support, DBT obviously does not have positive outcomes for all individuals. It is critical that cases of DBT nonresponse be analyzed so that further treatment development efforts can be made to enhance treatment outcomes for all individuals in DBT. Following an overview of DBT and its approach to the notion of "treatment failure," a detailed case example of unsuccessful treatment with a woman with severe BPD is provided. Analyses of possible reasons for the treatment failure, as it applies to the specific case and other DBT cases more broadly, are offered. Research and clinical implications are discussed.