This study aimed to test the diagnostic utility of the DNA integrity index for detection of cancer. Matched serum and plasma samples of 42 patients with various forms of cancer and 17 patients with corresponding benign diseases were analyzed. DNA was isolated from 1 mL serum and plasma using the MagNA Pure LC system. Cell-free DNA was quantified by real-time PCR using the reference gene of the LightCycler t(14;18) kit. Subsequently, the DNA integrity index was calculated as the ratio in relative abundance of 347-bp versus 137-bp PCR products. We found that DNA concentrations were not different in plasma (median: 4.5 ng/mL) and serum (67.1 ng/mL) of patients with benign diseases when compared with values in plasma (5.1 ng/mL) and serum (65.4 ng/mL) of cancer patients. Similarly, the DNA integrity index in plasma (0.38), and serum of patients with benign diseases (0.29) was comparable to values in plasma (0.33) and serum (0.37) of cancer patients. Diagnostic sensitivity of DNA (AUC 0.53) and DNA integrity (AUC 0.45) was poor in plasma, and was increased only slightly by the combination of both (AUC 0.57). In serum, sensitivity of DNA (AUC 0.52) and DNA integrity (AUC 0.64) was higher and was further improved by the combination of both (AUC 0.72) reaching a sensitivity of 30% at 100% specificity. In conclusion, we could not confirm a high diagnostic utility of the DNA integrity index. However, a combination with other markers such as DNA may enhance sensitivity for cancer detection.