We studied 73 patients treated with 3-dimensional conformal radiotherapy for prostate cancer to determine whether there is a correlation between dose per volume to either the whole rectum, rectal wall, rectal surface, or anal canal and the development of late rectal complications measured with prostate-specific quality-of-life (QOL) questionnaires. Given doses were 66.6 to 72 Gy. The prostate cancer modules used were the UCLA-Prostate Cancer Index module (UCLA-PCI) (5 questions), the Functional Assessment of Cancer Therapy-Prostate module (FACT-P) (1 question), and the European Organization for Research and Treatment of Cancer prostate cancer module (EORTC QLQ-PR25) (4 questions). A Spearman correlation analysis between the total toxicity score and the dose-volume histograms (DVHs) was performed. All statistical tests were 2-sided. Sixty-five (89%) patients returned the questionnaire, and 18 (28%) underwent endoscopy for rectal bleeding. We found that only patients who had had an endoscopy showed a correlation between rectal toxicity and dose per volume, as compared with the other patients who showed none. Correlation between rectal toxicity and dose per volume for all 4 structures was stronger for higher doses. For 70 Gy, all contours, except the anal canal, showed a significant dose-volume correlation. Our results indicate that only in cases of pronounced rectal toxicity is there a dose-volume correlation, especially for doses of 70 Gy or more. DVHs of the whole rectum, wall, or surface, but not the anal canal, are all equivalent in predicting late rectal toxicity.