Soc Psychiatry Psychiatr Epidemiol (2007) 42:288–294 O R I G I N A L P A P E R DOI 10.1007/s00127-007-0171-6 Sebastian Ko¨hler Æ Jim van Os Æ Ron de Graaf Æ Wilma Vollebergh Æ Frans Verhey Æ Lydia Krabbendam Psychosis risk as a function of age at onset A comparison between early- and late-onset psychosis in a general population sample Accepted: 26 January 2007 / Published online: 12 March 2007 j Abstract Background Little is known about late- onset psychosis (onset after the age 45 years) and how it relates to early-onset psychosis (before age 45 years). The aims of this study were to calculate the incidence of non-affective, non-organic psychotic symptoms across the life span and to explore the contribution of different sets of risk factors in relation to age at onset. Methods Data were obtained from the three measurements of the Netherlands Mental Health Survey and Incidence Study. Symptoms of psychosis were assessed in individuals aged 18–64 years using the Composite International Diagnostic Interview. All individuals reporting ﬁrst-onset of psychotic symp- toms within a three-year interval were included. The degree to which sets of risk factors affected the psy- chosis outcome similarly across age groups was as- sessed. Results The number of subjects displaying incident psychotic symptoms was similar across age groups. Cumulative incidence rates ranged from 0.3% to 0.4%. Age differences were found for life-time depressive symptoms (risk difference = 5%, 95% CI = 1%, 9%) and baseline neuroticism (risk differ- ence = 3%, 95% CI = 0%, 6%), indicating that late- S. Ko¨hler Æ J. van Os Æ F. Verhey Æ L. Krabbendam (&) Dept. of Psychiatry and Neuropsychology Sth Limburg Mental Health Research and Teaching Network, EURON Maastricht University P.O. Box 616 (VIJV) 6200 MD Maastricht, The Netherlands Tel.: +31-43/3688682 Fax: +31-43/3884092 E-Mail: l.krabbendam@sp.unimaas.nl J. van Os Division of Psychological Medicine Institute of Psychiatry London, UK 1 R. de Graaf Æ W. Vollebergh 17 The Netherlands Institute of Mental Health and Addiction PE Trimbos-Institute Utrecht SP Utrecht, The Netherlands onset psychosis was less often preceded by these. In contrast, no effect modiﬁcation by age was observed for female sex, hearing impairment, being single, or life-time cannabis use. Conclusions Onset of psy- chotic symptoms in late life is no rare event. Com- pared to early onset psychosis, the late-onset counterpart less often arises in a context of emotional dysfunction and negative affectivity, suggesting qualitative differences in aetiology and more effective premorbid coping styles. j Key words psychosis – late onset – risk factors – incidence – general population Introduction Schizophrenia and related non-affective, non-organic psychotic disorders have predominantly been studied in adolescence and young adulthood (early-onset psy- chosis, EOP). Some individuals, however, experience psychotic symptoms for the ﬁrst time after the age of 40 years (late-onset psychosis, LOP) [19, 29]. In LOP, the clinical picture is dominated by hallucinations in all modalities and systematic delusions that concern the patient’s personal space and security like paranoid delusions or partition delusions [8, 26, 27], while dis- organized and negative symptoms are uncommon [44, 53]. In 45% of subjects, the onset of LOP is preceded by a history of paranoid or schizotypic personality styles [31, 33, 45] which raises the question whether these cases constitute a group of schizophrenia with delayed expression of a latent disorder rather than truly late onset of a disorder de novo. j Incidence rates Studies of ﬁrst admission rates over the last four decades have consistently found low incidence rates