Background: To determine the prevalence of dementia among the residents of geriatric institutions in the greater Jerusalem area.

Methods: A population-based, cross-sectional survey of a representative sample, weighted according to the level of care, of 11 of the 88 long-term care (LTC) wards in 34 LTC institutions providing care for the elderly residents in the greater Jerusalem area in 1999. A single physician interviewed 311 residents. The presence of dementia was determined from medical records and by performance on the Modified Mini-mental State Examination (3MS) instrument (with a score less than 78/100 indicating significant cognitive impairment or suspected dementia), and professional care providers were interviewed for their opinion regarding the presence of dementia in each subject.

Results: The mean age of the patients was 83.9 years and 75% were women. Overall, 180 residents, representing 49.9% of the weighted sample in Jerusalem LTC facilities, were determined to have dementia according to medical records, ranging from 22.9% in independent and frail care units to 97.7% in skilled nursing care wards. However, based on their performance on the 3MS, the prevalence of cognitive impairment with suspected dementia among the subjects was substantially greater, with the staff being unaware of this diagnosis in about one-quarter of the subjects.

Conclusions: There is a high prevalence of dementia in geriatric institutions in the Jerusalem area, particularly in those providing greater care. Moreover, significant cognitive impairment is probably under-reported in the medical records.