Exercise habits and indices of aerobic fitness as measured by spiroergometric testing were examined in 38 patients with panic disorder and/or agoraphobia and 24 untrained healthy controls. Maximal oxygen consumption, maximal power output and the power output at a lactate concentration of 4 mmol/l were significantly reduced in the patient group when compared to untrained controls. Other parameters like physical work capacity at a heart rate of 150/min, maximal lactate concentration, vital capacity, subjective exertion at maximal work load, and maximal heart rate did not differ between patients and controls. Patient interviews revealed that aerobic exercise is avoided by the vast majority of patients. Reduced aerobic fitness might contribute to the pathophysiology of panic disorder and/or agoraphobia.