Classical progressive supranuclear palsy, also known as Richardson's syndrome, is the most common clinical variant of progressive supranuclear palsy (PSP), a rare late-onset neurodegenerative disease characterized by postural instability, progressive rigidity, supranuclear gaze palsy and mild dementia. The disease is Monarch Disease Ontology entry MONDO_0010997 (supranuclear palsy, progressive, 1). Also known as: PSP, Richardson syndrome, classic PSP syndrome, classic progressive supranuclear palsy syndrome, supranuclear palsy, progressive, supranuclear palsy, progressive, type 1.