Objective: To examine the association between Five Factor Model personality traits (Neuroticism, Extraversion, Openness to experience, Agreeableness, Conscientiousness) and physician-quantified aggregate morbidity in a sample of older adults in primary care. Methods: A total of 449 primary care patients, ranging in age from 65 to 97 years (75 +/- 6.9 (mean +/- standard deviation)), completed the Neo-Five Factor Inventory (NEO-FFI) and extensive interviews. A physician-investigator completed the Cumulative Illness Rating Scale (CIRS), a well-validated measure of aggregate morbidity based on a review of medical records. Results: Bivariate analyses demonstrated that all five domains of the NEO-FFI were associated with CIRS scores. Multivariate regression controlling for age, gender, education, depression, smoking, hypertension, total cholesterol, alcohol or substance misuse, and other personality traits showed that greater Conscientiousness was independently associated with lower CIRS scores (beta = -0.10, t(435) = -1.96, p = .05). Other independent predictors of less morbidity were younger age, absence of hypertension, and lower levels of depression. Conclusion: Our results point toward the necessity of considering Conscientiousness and other personality traits in studies of risk factors for aggregate morbidity. More detailed characterization of at-risk populations will increase the likelihood of constructing informed and effective prevention, intervention, and policy initiatives.