To find out whether weight reduction induced by vertical banded gastroplasty (VBG) alters the energy expenditure in severely obese women during treadmill walking. A prospective one year follow-up study, patients being their own controls. University hospital, Sweden. A consecutive series of 11 women who had VBG. Indirect calorimetry, body mass index (BMI), preset and comfortable walking speeds, heart rate, perceived exertion, and quality of life. 11 patients were evaluated. Mean BMI (kg/ml) decreased from 41 (range 36-46) before to 32 (range 25-37) 12 months postoperatively. The energy expenditure decreased significantly both at comfortable and preset walking speeds. The comfortable walking speed increased from 2.7 km x h(-1) (range 1.3-3.4) before operation to 3.8 (range 2.0-4.2) one year postoperatively (p = 0.003). All bodily variables in the SF-36 questionnaire showed improvement from 6 months onwards. Weight reduction in women reduces the energy expenditure during walking both at comfortable and preset speeds. The comfortable walking speed is increased. The improvements are reflected in the patients' own assessment.