Parkinson's disease (PD) is clinically characterized by symptoms of akinesia, rigidity, and resting tremor, which are related to a dopaminergic deficiency of the nigrostriatal pathway. Disorders of gait are common symptoms of PD that affect the quality of life in these patients. One of the main focuses of physical rehabilitation in PD is to improve the gait deficits in the patients. In the last decade, a small number of studies have investigated the use of the treadmill for the rehabilitation of gait in PD patients. Although, the results of these studies are promising, the mechanisms underlying the therapeutic effect of the treadmill in PD are still largely unknown. This paper reviews 10 years of investigation of treadmill training in PD, focusing on the possible mechanisms involved in the therapeutic effect of the treadmill. Understanding these mechanisms may improve the prescription and design of physical therapy programs for PD patients.