It remains a matter of conjecture as to whether a schizophrenia-like syndrome commencing in old age differs from the early-onset disorder in any substantial way. This article reviews both the historical background to the concept of defining paraphrenia as a distinct entity, as well as the current controversies concerning whether it should remain a separate entity: the latter is important as paraphrenia has not been included in the DSM Ill-R and ICD 10 classification systems. Clinical parameters and aetiological factors relevant to an understanding of the syndrome are discussed under the rubrics of descriptive and construct validity. Of particular importance are the role of cerebral organic factors and the pathoplastic effect of the ageing process and how both interface with the development of psychotic symptoms. Whilst the course of this syndrome has been considered relatively benign, outcome studies have yet to establish consistent features that provide a basis to determine predictive validity.