Failure to complete needed operations in the separation-individuation process during early childhood development is increasingly suspected of being a major source of borderline pathology. Building on Mahler's descriptions of this process as an interpersonal operation between child and mother, we have directly intervened in the patient-mother relationship in a small group of adult female borderlines. All patients displayed rapid and apparently complete clearing of borderline symptoms following limited conjoint therapy. Although neuroses remained, the criteria for a borderline diagnosis were no longer met. Treatment results with six women who had pretreatment and posttreatment psychological testing are reported. Testing confirmed clinical impressions of significant shifts in psychological defenses as well as perceptions of self and others. Fundamentals of this approach are discussed briefly, and observations regarding possible borderline pathology, mother-daughter interactions, family dynamics, and therapeutic philosophy are made. This approach appears not only to be effective but offers promise of simplifying both the role of the therapist and the therapy itself.