Cancer impairs spermatogenesis, whereas results on sperm DNA integrity are controversial and no data are available about sperm oxidative stress. In cancer patients, we detected sperm DNA fragmentation (sDF) and both viable (ROS production in viable sperm fraction/viable spermatozoa) and total (ROS production in viable sperm fraction/total spermatozoa) oxidative stress. We found that cancer (22.50 (17.00–26.75)%,n= 85) increased sDF with respect to the control groups in both normozoospermic subfertile patients (NSP) (12.75 (8.63–14.88)%,n= 52,p< 0.001) and in healthy donors (HD) (8.50 (7.00–14.00)%,n= 19,p< 0.001). The induction of viable oxidative stress (n= 96) with cancer was even higher: 36.60 (24.05–58.65)% versus 11.10 (8.63–14.90)% in NSP (p< 0.001) and 9.60 (8.00–14.03)% in HD (p< 0.001). Similar, albeit lower, differences were found for total oxidative stress. SDF sharply correlated to viable oxidative stress when we considered all subjects (cancer patients and controls) (r = 0.591,p< 0.001,n= 134), but no correlation was found when only cancer patients were studied (r = 0.200;p> 0.05,n= 63). In conclusion, cancer significantly increases sDF and sperm oxidative stress levels. Additional mechanisms to oxidative attack might be responsible for increased sDF in cancer patients. Because sperm oxidative stress might affect the outcomes of sperm cryopreservation, of cancer treatments and of sperm epigenoma, the detection of oxidative stress could be of help in managing the reproductive issues of cancer patients.