Introduction Interest in personality traits and their relationship to depression has grown in recent years. The Big Five model of personality is often used as the standard framework in which personality constructs can be better understood. The model includes: (1) Extraversion/Positive Emotionality, (2) Agreeableness, (3) Conscientiousness, (4) Emotional Stability versus Neuroticism, and (5) Openness/Intellect. However, there is growing interest in optimism since it has been linked to low Neuroticism and high Extraversion/Positive Emotionality (Sharpe et al 2011). Optimism, defined as the extent to which people hold generalized favorable expectancies for their future, is also inversely related to hopelessness, a risk factor for depressive disorders. Prior research suggests that optimists tend to have high Emotional Stability, Extraversion, Agreeableness, and Conscientiousness, resulting in a tendency toward better mental and physical health, adaptive behavior, and even lower mortality rates (Achat et al 2000 and Armbruster et al 2015). Optimism remains understudied in older adults, particularly as most of the prior research has explored optimism as a construct of Neuroticism and Extraversion in younger and middle-aged adults (Armbruster et al 2015). We aimed to examine the effects of optimism on acute treatment outcome in a group of older depressed adults initially treated with the antidepressant sertraline in an open-label fashion as part of Neurobiology of Late-Life Depression (NBOLD), a US National Institute of Mental Health (NIMH)- supported study at the University of Connecticut (UConn). We hypothesized that presence of high optimism would be associated with lower 12-week remission rates in older depressed sertraline-treated patients. Methods In this longitudinal cohort study, all subjects were enrolled in NBOLD and recruited from clinic referrals and newspaper advertisements. Inclusion criteria for depressed subjects were age 60 or above, ability to read and write English, Mini- Mental State Examination (MMSE) score 25 or greater and meeting criteria for major depression, single episode, or recurrent (DSM-IV-TR). A total of 74 subjects were included and were administered the Montgomery–Ǻsberg Depression Rating Scale (MADRS) and Cumulative Illness Rating Scale (CIRS), as modified for geriatric patients. Each subject completed several self-report measures, including the Life Orientation Test- Revised (LOT-R, Scheier et al 1994), which measures total optimism. We used regression analyses to examine factors related to 12-week remission of depression (MADRS score Results We found that higher total optimism was not associated with lower likelihood of remission among both the intention-to-treat group and sertraline completers after controlling for baseline MADRS and CIRS score. Additional regression analyses of optimism, neuroticism and apathy were also examined, but were not associated with lower likelihood of remission. Conclusions Our results do not support that optimism alone can predict depression outcomes in older adults. Although optimism has been shown to have predictive value in younger and middle-aged adults, there may be other medical comorbidities such as somatic illness, as well as increasing psychosocial stressors, contributing to the development of late life depression that override the effects of optimism. This may explain why optimism, although important in older age, may not have strong predictive accuracy for health-related outcomes. Our findings are consistent with a prior study examining optimism and depression outcomes in younger vs older adults in which predictive accuracy decreases with age (Armbruster et al 2015). This research was funded by: Neurobiology of Late-Life Depression (NBOLD), a US National Institute of Mental Health (NIMH)- supported study at the University of Connecticut (UConn)