At baseline, three defenses were found in multivariate analyses to be significantly associated with a borderline diagnosis. Two of these defenses were immature and one was neurotic: acting out, emotional hypochondriasis (i.e., transformation of feelings of sorrow, rage, and terror into unremitting complaints about the lack of understanding that others display), and undoing. At 16-year follow-up, borderline patients could still be differentiated from Axis II comparison subjects, and improvement was found in many defenses. In addition, four time-varying defense mechanisms were found to predict time-to-recovery. One was mature and three were immature: humor, acting out, emotional hypochondriasis, and projection. The clinical meaning and usefulness of assessing defenses over time, particularly immature defenses, in clinical settings is discussed.