Many psychoanalytic writers have viewed acting out and somatization as alternate routes for the discharge of uncontained aggressive impulses in borderline patients. In order to investigate this empirically, we tracked the occurrence of two related behaviors—acting up and physical illness—over the course of one patient's long-term hospitalization. Daily scores on these variables were analyzed using a time series procedure. Results indicated that as treatment progressed, acting up and physical illness became more synchronized, and this occurred just prior to symptom remission. Material from psychotherapy suggested that these behavioral changes were associated with the patient's increased ability to verbalize aggressive impulses in the context of fantasy and memory.