Previous studies of posture in Parkinson's disease (PD) patients focused on the pathophysiology of severe deformities, using mainly subjective estimations or goniometric measures. The aim of this study was to investigate risk factors associated with flexed posture in PD and their effects on the course of posture variations. One hundred-ninety patients with definite PD were prospectively evaluated for angles of spinal inclination in upright position, extension, and flexion using a mechanical computer-assisted, hand-held device (SpinalMouse). Patients underwent clinical examination, including background data and bone mineral density. Motor function was evaluated with the UPDRS, and back pain with the RMDQ. Physical activity data were collected by self-report. Postural measurements were repeated after 10-17 months. Angle of upright inclination correlated with age (p = 0.0004), older age at disease onset (p = 0.0085), longer disease duration (p = 0.003), higher UPDRS motor and posture score (p = 0.0005 and 0.0001), the presence of back-pain (p = 0.0097), and osteoporosis (p = 0.027). There was no correlation between upright angle of inclination and gender, disease type, or side of disease onset. Re-evaluation of posture in 124 patients at 13.77 +/- 4.4 months after the initial evaluation showed significant deterioration in forward bending (p < 0.0001) and was significantly associated with disease duration (p = 0.029), worsening of the UPDRS score (p = 0.016), right-side disease onset (p = 0.032), presence of vertebral fractures (p = 0.049), and the lack of physical activity (p = 0.0327). Older age, disease severity and duration, presence of back-pain and osteoporosis are associated with postural abnormalities in PD. Physical activity might slow the worsening of postural abnormalities in PD.