Objectives: To investigate the prevalence of depression among the oldest old and to analyze factors associated with depression.

Methods:A cross-sectional, population-based study was undertaken in Umeå, Sweden. Out of 319 eligible participants aged 85, 90 and 95 years and older, it was possible to evaluate 242 people (75.9%) for depression. Data were collected from structured interviews and assessments in the participants’ homes, and from medical charts, relatives and caregivers. Depression was screened for using the Geriatric Depression Scale-15 and further assessed with the Montgomery–Åsberg Depression Rating Scale. Cognition was assessed using the Mini-mental State Examination, activities of daily living (ADL) using the Barthel ADL Index, nutrition using the Mini Nutritional Assessment and well-being using the Philadelphia Geriatric Center Morale Scale.

Results:The 85-year-olds had a significantly lower prevalence of depression than the 90- and 95-year-olds (16.8% vs. 34.1% and 32.3%). No sex differences were found. One-third of those with depression had no treatment and among those with ongoing treatment 59% were still depressed. Persons diagnosed with depression had a poorer well-being and a higher 1-year mortality. Logistic regression analyses showed that depression was independently associated with living in institutions and number of medications.

Conclusion:Depression among the oldest old is common, underdiagnosed and inadequately treated, and causes poor well-being and increased mortality. More knowledge about depression is essential to improve the assessment and treatment of depression among the oldest old.