Cancer-related fatigue is one of the most debilitating side effects of cancer and cancer therapy. We aimed to investigate co-occurring symptoms associated with persistent fatigue in men receiving external beam radiation therapy (EBRT) for nonmetastatic prostate cancer.A sample of 47 men with prostate cancer scheduled to receive radiotherapy (RT) were followed at baseline and 1 year after RT. Clinical and demographic data were obtained from chart review. Symptom measurements included urinary dysfunction (American Urological Association symptoms score), fatigue (Functional Assessment of Cancer Therapy - Fatigue questionnaire), sleep disturbance (Patient-Reported Outcomes Measurement Information System - Sleep Disturbance form), pain (physical well-being domain pain item of the Functional Assessment of Cancer Therapy - General), and depressive symptoms (Hamilton Depression Rating Scale). Paired t tests, correlations, general linear models, and logistic regressions were used to determine associations between fatigue and other symptom scores.At 1 year after RT, 34% of subjects continued to experience fatigue. Urinary dysfunction was the best clinical predictor of persistent fatigue. Pain and depressive symptoms further improved the predictive power of the model. A multivariate linear regression model containing all these three clinical variables (urinary dysfunction, pain, and depressive symptoms) explained 74% of total variance associated with persistent fatigue after RT.Persistent fatigue at 1 year after EBRT in prostate cancer survivors is likely related to a cluster of symptoms elicited by chronic inflammation. Therapies that target each of these symptoms will likely reduce fatigue in this patient population.