A measure that captures the frequency and intensity of experienced dysfunctional behaviors as well as the use of mental health services was developed and tested as part of a treatment controlled trial of patients with borderline personality disorder. The Objective Behavioral Index (OBI) was completed by 136 subjects with the diagnosis of borderline personality disorder before random assignment to treatment and by 35 subjects at each follow-up point. With one exception, the OBI subindexes (Dysfunctional Behaviors and Service Utilization) were not intercorrelated nor were they associated with any of the other patient status measures. Both of the OBI subindexes were sensitive to change after a course of psychotherapy. The OBI measurement system is easy to use and provides important information about behavioral dysfunction and service utilization. Also, contrary to expectations, service utilization is not associated with patient symptomatic and behavioral status.