Thirty-seven, out of a sample of 100 elderly subjects, all suffering from dementia, were found to have delusions. The delusions were more common in women, in patients with a history of psychiatric illness, and amongst those with higher information subscores (Blessed Scale); and were less common in patients suffering from apraxia or severe psychosocial incompetence. Amongst the deluded patients the simultaneous presence of disorientation, hallucinations and hyperactivity often signified the diagnosis of delirium, but on follow up it was not correlated with death within 18 months. The same symptoms in the non-deluded patients were correlated with severe social incompetence and death within 18 months. It is concluded that the presence of delusions in subjects over 75 years old suffering from dementia is related, to certain extent, to previous or concomitant psychiatric illness, and that it reflects a relative preservation of mental function amongst those without such history.