The influence of dementia on the prevalence of urinary and faecal incontinence was investigated in a random sample (n = 485) of the total population of 85-year-olds from the city of Gothenburg, Sweden, The subjects were assessed by a psychiatric interview, physical examinations, computed tomography of the head and analysis of cerebrospinal fluid. Urinary and faecal incontinence were assessed by a urotherapist. Dementia, urinary and faecal incontinence were defined according to strict, internationally accepted criteria. The prevalences of urinary and faecal incontinence, and dementia were 38%, 17% and 29% respectively. Demented men (50%) and women (60%) were more often urinary incontinent than non-demented men (18%) and women (36%). Faecal incontinence was more prevalent in demented (34.8%) than non-demented subjects (6.7%). Both urinary and faecal incontinence were more prevalent in women (43% and 20% respectively) than men (27% and 11%, respectively). The prevalences of urinary and faecal incontinence, and dementia were higher in residents;of a nursing home or hospital (74%, 51% and 92%, respectively) than in subjects living at home (32%, 9% and 18%, respectively). Of the demented subjects resident in an institution, 78% were incontinent compared with 37% living at home. Incontinence aids were used by 18% of the men and 33% of the women, and their use increased with increasing severity of dementia. Dementia influenced the prevalence of urinary incontinence, and both conditions independently of each other strongly influenced the need for institutional care.