The most important features that characterize and differentiate progressive supranuclear palsy from other Parkinsonian syndromes are postural instability, supranuclear gaze palsy, pseudobulbar palsy, parkinsonism, and cognitive disturbances. In this article, we demonstrate that progressive supranuclear palsy patients exhibit pathologically decreased pupil diameters after dark adaptation recorded by TV pupillography. A cut off value of 3.99 mm was defined to differentiate progressive supranuclear palsy patients from patients with other extrapyramidal disorders like Parkinson's disease and multiple system atrophy with a specificity of 86.4% and a sensitivity of 70.8%. Other pupil abnormalities could not be described in patients with extrapyramidal syndromes.