Classical progressive supranuclear palsy (Orphanet rare-disease nomenclature term Orphanet_240071), also known as Richardson's syndrome, is the most common clinical variant of progressive supranuclear palsy (PSP; see this term), a rare late-onset neurodegenerative disease characterized by postural instability, progressive rigidity, supranuclear gaze palsy and mild dementia. Also known as: Classical PSP, Richardson syndrome, Steele-Richardson-Olszewski disease.