Apart from well-known and proven consequences such as motor symptoms in Parkinson's disease and dementia in Alzheimer's disease, the neurological consequences of these diseases also cause cognitive and linguistic changes. People with Parkinson's disease have obvious deficits in reading physical books due to broken hand motion, inability to manipulate fingers and joints, and shaking their hands making them trouble turning pages. The same deficits give rise to difficulties in the performance of writing skills causing micrographia. In addition, reading difficulties occur due to impaired visual processing, and problems arise also with the reading comprehension. In Alzheimer's disease, difficulties occur at the level of phonology and semantics, the lexical orthographic processing and visual processing are disturbed which is all reflected in reading in this population. During the act of writing, planning, sequencing, and organization at the level of letters, words, sentences and performance at narrative levels is disturbed. The range and complexity of the grammatical structures is also weakened.Difficulties in reading and writing have been shown to be a sensitive indicator of language dysfunction in Parkinson's and Alzheimer's disease. Understanding the deficit at different levels of reading and writing can help speech and language pathologysts to develop therapy strategies and improve the overall communication and functioning of the people of this population.