This chapter considers memory functioning in patients with primary degenerative dementia, degenerative dementia associated with other neurological conditions, patients with CNS demyelination and patients with evidence of progressive cognitive dysfunction due to hydrocephalus. The term ‘dementia’ can sometimes be misleading, since it is occasionally used to refer to an impaired level of cognitive functioning (and as such could be used with reference to any clinical aetiology), or it is used in the form of a predictive diagnosis, often implying a specific degenerative pathology. In addition, because of the lack of commonly agreed and valid instruments for the assessment of cognitive deterioration, even those studies of patients from within a specific aetiology may not be strictly comparable, since the progressive nature of the disease can result in differences in severity and pattern of memory deficits depending on the stage of illness at which patients are examined (e.g. Corkin, 1982; Oberer al., 1985).