We devised a Progressive Supranuclear Palsy (PSP) Rating Scale comprising 28 items in six categories: daily activities (by history), behaviour, bulbar, ocular motor, limb motor and gait/midline. Scores range from 0 to 100, each item graded 0-2 (six items) or 0-4 (22 items). Inter-rater reliability is good, with intra-class correlation coefficient for the overall scale of 0.86 (95% CI 0.65-0.98). A single examiner applied the PSPRS at every visit for 162 patients. Mean rate of progression was 11.3 (+/-11.0) points per year. Neither onset age nor gender correlated well with rate of progression. Median actuarially corrected survival was 7.3 years. The PSPRS score was a good independent predictor of subsequent survival (P < 0.0001). For example, for patients with scores from 40 to 49, 3-year survival was 41.9% (95% CI 31.0-56.6) but 4-year survival was only 17.9% (95% CI 10.2-31.5). For those patients, likelihood or retaining some gait function was 51.7% (40.0-66.9) at 1 year but only 6.5% (1.8-23.5) at 3 years. We conclude that the PSPRS is a practical measure that is sensitive to disease progression and could be useful as a dependent variable in observational or interventional trials and as an indicator of prognosis in clinical practice.