A randomized clinical trial was conducted to evaluate the effectiveness of a cognitive-behavioral therapy, ie, dialectical behavior therapy, for the treatment of chronically parasuicidal women who met criteria for borderline personality disorder. The treatment lasted 1 year, with assessment every 4 months. The control condition was "treatment as usual" in the community. At most assessment points and during the entire year, the subjects who received dialectical behavior therapy had fewer incidences of parasuicide and less medically severe parasuicides, were more likely to stay in individual therapy, and had fewer inpatient psychiatric days. There were no between-group differences on measures of depression, hopelessness, suicide ideation, or reasons for living although scores on all four measures decreased throughout the year.