Gait disturbances are frequent in Parkinson's disease (PD) and are associated with increased energy expenditure during walking. This study evaluated whether the effects of treadmill training are associated with an improvement of walking economy. Ten patients with idiopathic PD underwent treadmill training (30 min, three times a week for 4 weeks). Walking performance (Tauimed Up and Go, 6-min and 10-m walking tests) and metabolic function (oxygen uptake, heart and respiratory rate) were evaluated before training, at the end of treatment and after 30 days with two different graded exercises (treadmill and cycloergometer). Training significantly improved walking performance. Oxygen uptake, and heart and respiratory rates were significantly decreased only during graded exercise on the treadmill, but not on the cycloergometer. Treadmill training reduces energy expenditure during walking in PD, but the improvements of metabolic walking economy are associated with the specifically trained motor activity.