['A comprehensive understanding of the role of modifiable health behaviors in effective management of cancer-related fatigue is needed. Among breast cancer survivors, we examined how postdiagnosis diet quality, independently and jointly with physical activity, is related to fatigue, and the potential mediating role of inflammation.', 'Seven hundred seventy women diagnosed with stage 0-IIIA breast cancer in the Health, Eating, Activity, and Lifestyle study completed food frequency and physical activity questionnaires 30 months postdiagnosis. We scored diet quality using the Healthy Eating Index 2010 (HEI-2010). Serum concentrations of C-reactive protein (CRP) were measured in fasting 30-ml blood samples. Multidimensional fatigue was measured 41 months postdiagnosis using the 22-item revised Piper Fatigue Scale. In multivariate linear models, we determined whether fatigue was associated HEI-2010 quartiles (Q1-Q4), and a variable jointly reflecting HEI quartiles and physical activity levels.', 'Survivors with better-quality diets (Q4 vs. Q1) had lower total fatigue (4.1 vs. 4.8, p-contrast\u2009=\u20090.003) and subscale scores (behavioral severity 3.4 vs. 4.2, p-contrast\u2009=\u20090.003; affective meaning 3.9 vs. 4.8, p-contrast\u2009=\u20090.007; sensory 4.4 vs. 5.2, p-contrast\u2009=\u20090.003; cognitive 4.6 vs. 5.0, p-contrast\u2009=\u20090.046). Least squares estimates of fatigue were similar in models including CRP. Compared to survivors with poor-quality diets and no physical activity, survivors with better-quality diets and meeting physical activity recommendations had significantly lower behavioral severity (3.2 vs. 4.7, p-contrast\u2009=\u20090.002) and sensory (3.8 vs. 4.8. p-contrast\u2009=\u20090.006) fatigue scores.'] Is better postdiagnosis diet quality associated with less cancer-related fatigue in breast cancer survivors?