Patient reluctance to report pain has been shown to be a primary reason for inadequate pain control among cancer patients. Very little is known about whether patients' self-reports of pain vary by treatment settings. We reviewed 63 medical records of female breast cancer patients who visited two treatment settings on the same day in a tertiary cancer center in the United States. Patients' rating of pain (on a 0 [no pain]-10 scale) were abstracted. Results showed discrepancies regarding patients' self-reports of pain intensity in the two treatment settings. Fifty-one percent of patients' self-report of pain differed between the two treatment settings, with 38% reporting a pain score > or =4 in the outpatient breast clinic and =0 in the outpatient chemotherapy clinic. Although it is expected that pain may vary on a sporadic or activity-related basis, these results may also indicate the need to review clinic staffs' methods of assessing patients about their pain and a review of documentation practices of pain assessment.