Effects of Behavioral Activation Treatment (BAT) on pain anxiety, depression, and pain interference on a 43-year-old female with an 11-year history of chronic fibromyalgia pain are described. Analgesic, anxyiolytic, and antidepressant medications were stabilized prior to participation. Dependent measures were the Behavioral Relaxation Scale, a direct observation measure of relaxed behavior, and self-report measures of depression, pain anxiety and pain interference. A within session pre-post training assessment, embedded in a multiple-baseline-across-relaxed-positions single-subject experimental design, was used. BAT, based on the matching law, was comprised of behavioral relaxation training (BRT), activity-relaxation cycles, engaging in valued activities, and visual feedback of functioning. BRT resulted in an immediate increase in reclined relaxed behaviors with generalization to the upright relaxed position. A 100% improvement from baseline pain interference ratings was obtained following BAT. All four dimensions of pain anxiety declined to normative levels following BAT. Pain anxiety cognition declined without direct intervention. Depression declined to normative levels. Medication usage decreased from beginning to end-of-intervention but rose at follow up. Results were maintained at three-month follow up. Pain anxiety cognition was conceptualized verbal behavior that functioned as an establishing operation (EO) affecting consequences of overt and visceral (emotional) pain behavior. Altering contingencies related to overt healthy behavior delimits the effectiveness of the EO. Further research on BAT and pain anxiety cognition EOs is needed with chronic pain patients with fibromyalgia. (Contains 4 figures.)