OBJECTIVE: Dementia is a major public health problem among the elderly in developed countries and a growing problem in the underdeveloped countries. There are no published data on dementia in any of the Arabic countries. The aim of this study was to determine the different sub-types of dementia among Qataris. METHODS: A retrospective and prospective ongoing hospital-based study in which all medical records of the patients with diagnosis of dementia seen at the Hamad General Hospital, Doha, Qatar, between June 1997 and June 2003, whether inpatient or outpatient were reviewed. Dementia was defined according to diagnostic and statistical manual (DSM) IV criteriThose who had dementia were evaluated by a psychologist, psychiatrist, neurologist and a geriatrician. All had brain computerized tomography, magnetic resonance imaging or both and routine blood tests. Finally, they were classified into sub-types according to the cause of dementiRESULTS: Out of 300 patients, 134 fulfilled the inclusion criteria, most of them were illiterate, married and non-smokers. Among those dementia sub-types were: Alzheimer disease (AD) 39 (29%), vascular dementia (VaD) 30 (22%), mixed AD and VaD 20 (15%) and Parkinson's disease with dementia 8 (6%) were noted. The rest of them had dementia due to other medical conditions. CONCLUSION: Our study showed that AD is more prevalent than VaD. It also showed that patients and their families seek medical help late due to the general belief among the public that forgetfulness and other associated cognitive impairment are part of the normal aging process. The emergence of new drugs and advancement in the prevention of cerebrovascular diseases makes early diagnosis of dementia sub-type important. A community based study, to show the real prevalence and incidence of sub-types of dementia, is highly indicated. These data are necessary for planning and setting up community services and health care programs for demented patients.