Analysis of cerebrospinal fluid is important in the diagnostic evaluation of cognitive impairment and dementia and may help to identify possibly reversible conditions as summarised in this review. Moreover, analysis of specific molecules such as beta-amyloid, phosphorylated tau and neurofilament light chain may contribute to the diagnosis of neurodegenerative diseases including Alzheimer's disease. A number of promising candidate fluid biomarkers are currently under development and may in future improve accuracy of diagnosis and point towards a molecular-based diagnosis of neurodegenerative dementia disorders.