Journal article: Objectives This study aimed to analyze the behavioral determinants of breast cancer (BC) diagnosis delays in France. To do so, we investigated whether time discounting, risk tolerance, and personality traits influenced the BC diagnosis delay of patients. Methods We used original retrospective data collected on 2 large online patient networks from 402 women diagnosed of BC. The BC diagnosis delay was measured by the difference between the date of diagnosis and the date of first symptoms. Time discounting and risk tolerance are measured with both self-reported questions and hypothetical lotteries. Personality traits are measured with the 10-item Big Five indicator. Ordinary least square and probit models were used to analyze whether these behavioral characteristics influenced the BC diagnosis delay. Results Results showed that risk tolerance and time discounting were not significantly associated with the BC diagnosis delay. However, we found a longer diagnosis delay for women with a neuroticism personality trait (standardized coefficients ranged from 0.104 [P-value = .036] to 0.090 [P-value = .065]). Conclusions Overall, our findings underline the need for an increased consideration of cancer screening public health policy for women with mental vulnerabilities since such vulnerabilities were found to be highly correlated with a neuroticism personality trait.