Progressive supranuclear palsy (PSP) is a distinct clinicopathological entity characterized by neurofibrillary tangles, tufted astrocytes, threads and oligodendroglial coiled bodies. These four lesions are distributed in varying densities throughout subcortical and brainstem structures. There is no data regarding the relationship of disease duration to lesion burden severity in PSP. We report the results of analysis of semiquantitative data collected as part of the diagnostic evaluation on 97 cases of 'pure' PSP, submitted to the Society of PSP Brain Bank. Surprisingly, the data suggests that in PSP as duration of illness increases there is a decrease in oligodendroglial tau burden.