Background: Blood-based DNA integrity, defined as the relation of long to small fragments of cell-free circulating DNA, is known to be increased in various types of cancers. Since different DNA fragments and formulae are used by different researchers, conflicting results on the relevance of this marker for cancer diagnosis have been reported. Patients and Methods: Sera from 24 patients with colorectal cancer, 11 patients with benign gastrointestinal diseases, and 24 healthy individuals were investigated. After DNA isolation, ALU repeats with 115 bp and 247 bp length were measured using quantitative polymerase chain reaction and resulting DNA integrities were calculated by the two formulae of Umetani et al. (DNA Int 1) and Wang et al. (DNA Int 2) Results: DNA integrity by both formulae correlated strongly with each other. DNA integrity was significantly higher in patients with colorectal cancer when compared with healthy controls (p=0.005 and p=0.006, respectively), while there was no significant difference from those with benign colorectal diseases. In receiver operating characteristic curve analysis, areas under the curve of 0.74 and 0.73 and sensitivities of 71% at 75% specificity (DNA Int 1 and 2, respectively) were achieved for the discrimination between patients with colorectal cancer and healthy controls. Conclusion: DNA integrity is significantly increased in patients with colorectal cancer and may be useful in prospective trials.