OBJECTIVE The purpose of this study was to investigate the impact of race and obesity on dose and dose intensity of adjuvant chemotherapy. METHODS We abstracted data on patient/tumor characteristics, treatment course, physicians' intention to give a first cycle dose reduction, and reasons for dose reductions/delays from oncology records of 489 women treated from 1985 to 1997 in 10 treatment sites in two geographical regions. Administered doses and dose intensity were compared to standard regimens. Multivariate regression models determined the impact of race and body mass index (BMI) on dose proportion (actual:expected doses) and relative dose intensity (RDI) controlling for patient characteristics, comorbidity, chemotherapy regimen, site, and year of treatment. Logistic regressions explored race and BMI versus use of first cycle dose reductions. RESULTS African-Americans received lower chemotherapy dose proportion and RDI than whites (0.80 vs. 0.85, p = 0.03 and 0.76 vs. 0.80, p = 0.01). In multivariate analyses, dose proportion was 0.09 lower (p = 0.002), and RDI was 0.10 (p < 0.001) lower in non-overweight African-Americans than whites. Obesity was associated with lower dose proportion (p < 0.01) and RDI (p < 0.03). Race and BMI were independently associated with first cycle dose reductions. Non-overweight African-Americans (p < 0.05) and overweight and obese African-American and white women (p < 0.001) were more likely to have first cycle dose reductions than non-overweight whites. CONCLUSIONS We identified systematic differences in the administration of chemotherapy given to African-Americans and to overweight and obese women. These differences may contribute to documented disparities in outcome.