The present study had three objectives: (a) to characterize the functional capacity of patients with PD, (b) to assess the relationship between the physical fitness components of functional capacity with clinical characteristics and disease severity, and (c) to compare the physical fitness components of functional capacity with clinical characteristics according to disease severity. The study included 54 patients with idiopathic PD who were distributed into two groups according to PD severity: unilateral group (n= 35); and bilateral group (n= 19). All patients underwent psychiatric assessment by means of the Hoehn and Yahr (HY) staging of PD, the Unified Parkinson's Disease Rating Scale (UPDRS), the Hospital Anxiety and Depression Scale (HADS-A and HADS-D, respectively), and The Mini-Mental State Examination (MMSE). The physical fitness components of functional capacity were evaluated over a 2-day period, using recommendations by the American Alliance for Health, Physical Education, Recreation and Dance, and the Berg Balance Scale (BBS). Pearson correlation coefficients and multiple regressions were calculated to test the correlation between functional capacity and clinical characteristics, and to predict clinical scores from physical performance, respectively. Clinical variables and physical component data were compared between groups using analysis of variance to determine the effects of disease severity. Patients with advanced disease showed low levels of functional capacity. Interestingly, patients with good functional capacity in one of the physical fitness components also showed good capacities in the other components. Disease severity is a major factor affecting functional capacity and clinical characteristics. Medical providers should take disease severity into consideration when prescribing physical activity for PD patients, since the relationship between functional capacity and clinical characteristics is dependent on disease severity.