A sample of 126 elderly persons with cognitive impairment who were living in the community were clinically assessed for severity on a range of illnesses: somatic, psychiatric, neurodegenerative. At the same time, their disability was examined by self-report and via informant report. The domains of disability that were investigated were personal care, instrumental activities and social functioning. The key findings were that most of the variation in disability in each domain was accounted for by the clinical diagnoses. Analysis of informant data (N = 90) showed that social functioning was affected by behavioural impairment and depression, performance in instrumental activities was affected by extrapyramidal gait disorder, cognitive impairment, behavioural impairment and depression, while personal care was affected by extrapyramidal gait disorder, cognitive impairment, depression and arthritis. Similar results were obtained with subject data (N = 126) on scales of instrumental activities and personal care: disability in instrumental activities was associated with diagnoses of extrapyramidal gait disorder, cognitive impairment, behavioural impairment and stroke, while personal care was affected by extrapyramidal gait disorder, peripheral vascular disease and stroke. In this population, neuropsychiatric disturbances (disorders of cognition, behaviour and mood) and extrapyramidal gait disorders are major independent predictions of disability. Somatic disorders have a lesser impact.