['This study aims to compare the performance status assessed by breast cancer patients and their oncologist and investigate the factors associated with the patient-oncologist disagreement in a multi-ethnic Asian population.', "This is a cross-sectional study of 270 female breast cancer patients in Singapore. Patients' performance status was rated by the patients and their treating oncologists. Patients were also asked to complete two instruments regarding their health status and health-related quality of life. The proportions of patients with assessment of performance status the same as and different from their oncologist were calculated. The level of agreement was quantified by Kappa statistics together with the confidence interval (CI). Multinomial logistic regression analyses were performed to examine potential factors associated with the patient-oncologist disagreement.", "Approximately half (136/270) of the patients agreed with the oncologist in assessing performance status. Among the disagreeing half, 48 (17.8 %) patients rated better and 86 (31.9 %) poorer than the oncologists. The unweighted and quadratic-weighted Kappa statistics were, respectively, 0.21 (95 % CI\u2009=\u20090.13 to 0.29) and 0.34 (95 % CI\u2009=\u20090.26 to 0.42). Multivariable multinomial logistic regressions showed that outpatient, language used, and evidence of disease were associated with patients' better assessment than the oncologists, while age, physical well-being, and pain/discomfort were associated with patients' poorer assessment."] Are patient-reported outcomes associated with patient-oncologist agreement of performance status in a multi-ethnic Asian population?