The aim of the study was for the first time to examine whether adults diagnosed with Borderline Personality Disorder feel that their sense of security improved through treatment with Dialectical Behavioral Therapy conducted one or two years earlier. In the current study perceived security was defined as a feeling of being free of worrisome or threatening phenomena. Twenty-three patients (2 men and 21 women) aged 18 to 57 years, were recruited from five teams in Southwest Sweden. A questionnaire was constructed where responses were given on visual analogue scales. There were three questions about security, namely perceived security when completing the questionnaire as well as estimated perceived security before and after treatment. The three questions were embedded among 19 other questions which dealt with various aspects of quality of life. Results indicated three main results: (a) the patients reported feeling more secure following the treatment, (b) mental health of the patients and their health in a broader view appeared to be decisive for the perception of security and (c) the perception of greater security remained one or two years following treatment. The conclusion was that perceived feeling of security might be able to add a new dimension to currently used ways to assess the effects of the treatment of borderline patients and it might also be considered to be included in a future concept of borderline remission.