Patients and physicians often disagree in their assessment of pain intensity. This study explores the impact of patient factors on underestimation of pain intensity in chronic noncancer pain. We surveyed patients and their physicians in 12 primary care centers. To measure pain intensity, patients completed an 11-point numeric rating scale for which pain scores range from 0 (no pain) to 10 (unbearable pain). Physicians rated patients' pain on the same scale. We defined disagreement of pain intensity as underestimation or overestimation by 22 points. Of 601 patients approached, 463 (77%) completed the survey. The majority of participants were black (39%) or white (47%), 67% were female, and the mean age was 53 years. Physicians underestimated pain intensity relative to their patients 39% of the time. Forty-six percent agreed with their patients' pain perception, and 15% of physicians overestimated their patients' pain levels by > or =2 points. In both the bivariate and multivariable models, black race was a significant variable associated with underestimation of pain by physicians (p < 0.05; OR = 1.92; 95% CI: 1.31-2.81). This study finds that physicians are twice as likely to underestimate pain in blacks patients compared to all other ethnicities combined. A qualitative study exploring why physicians rate blacks patients' pain low is warranted.