Neurofibrillary tangles are twisted, disfigured cytoplasmic filaments found in cortical neurons. They contains altered intermediate filaments. They can be demonstrated by special silver staining methods. Together with neuritic plaques, they constitute the histological substrates of Alzheimer's disease.

Although they can be seen in some other neurodegenerative diseases, their quantity in the brains of patients with Alzheimer's disease correlates better with cognitive functions than the number of neuritic plaques.