Introduction– Presently, there is a progressive increase in the geriatric population which demands the mental health care setup because mental illness is common in this population. Delirium in elderly is common but its aetiology poorly studied in geriatric mental health care setup.

Aim– To study aetiology of delirium in elderly patients admitted in Department of Geriatric Mental Health and comparing aetiological differences in patients with and without dementia.

Methods– Sixty patients admitted consequently in Department of Geriatric Mental Health and diagnosed case of delirium as per DSM–Ⅳ TR criteria, were recruited in study. Aetiology of delirium was assessed by physical examination, biochemical investigations and neuroimaging. Aetiologies of delirium were compared in patients with and without dementia. Underlying dementia screened using Informant Questionnaire on Cognitive Decline–short form (IQCODE–sf)

Results– Among all cases of delirium, twenty–one patients (35%) were having underlying dementia. Psychotropic drugs, urinary tract infection and constipation were most common causes of delirium in patients with dementia while respiratory tract infection, hyponatremia and acute stroke were most common cause of delirium in patients without dementia. All seven cases delirium due to stroke were having left sided stroke.

Conclusion– There are differences in aetiology of delirium in patients with and without dementia, which should be considered in prevention and management of delirium. Patients presenting with delirium, left sided stroke should be suspected even in absence of sensory or motor deficit.