The purposes of the study were to examine the concordance between patients' and family caregivers' assessments of patients' symptoms, and to identify demographic and psychosocial factors that affect levels of agreement. Sixty-six patients with advanced cancer receiving palliative care, and their primary, informal caregivers assessed patients' symptoms using the Memorial Symptom Assessment Scale (MSAS). Levels of agreement for individual symptoms ranged from poor to excellent (interclass correlation coefficient 0.07-0.75). Analysis of the group means using paired t-tests revealed significant differences for the MSAS subscales (psychological, physical, and general distress index), and for four of the 12 physical symptoms and five of the six psychological symptoms. The magnitude of the observed differences indicated a small to moderate bias for caregivers to overestimate, which was more marked for psychological than for physical symptoms. A number of factors associated with the caregiver (particularly the emotional state, the burden of providing care, and male gender) and the patient (the perception of being a burden to others) were significantly correlated with levels of disparity on some measures. The findings are consistent with the growing body of literature on the validity of proxy respondents' assessments of patients' symptoms.