Hoehn and Yahr scale
The Hoehn and Yahr scale is a commonly used system for describing how the symptoms of Parkinson's disease progress. It was originally published in 1967 in the journal Neurology by Margaret Hoehn and Melvin Yahr and included stages 1 through 5. Since then, a modified Hoehn and Yahr scale was proposed with the addition of stages 1.5 and 2.5 to help describe the intermediate course of the disease.
| Stage | Hoehn and Yahr Scale | Modified Hoehn and Yahr Scale |
| 1 | Unilateral involvement only usually with minimal or no functional disability | Unilateral involvement only |
| 1.5 | - | Unilateral and axial involvement |
| 2 | Bilateral or midline involvement without impairment of balance | Bilateral involvement without impairment of balance |
| 2.5 | - | Mild bilateral disease with recovery on pull test |
| 3 | Bilateral disease: mild to moderate disability with impaired postural reflexes; physically independent | Mild to moderate bilateral disease; some postural instability; physically independent |
| 4 | Severely disabling disease; still able to walk or stand unassisted | Severe disability; still able to walk or stand unassisted |
| 5 | Confinement to bed or wheelchair unless aided | Wheelchair bound or bedridden unless aided |
This rating system has been largely supplanted by the Unified Parkinson's Disease Rating Scale, which assesses limitation of daily activities and non-motor symptoms in more detail.
Time between stages
A 2010 study of 695 patients found the median time taken to transit H&Y stages as shown below:| Stage | Median Time to Transit |
| 1 | - |
| 2 | 20 |
| 2.5 | 62 |
| 3 | 25 |
| 4 | 24 |
| 5 | 26 |