Chemotherapy and radiotherapy adversely affect spermatogenesis, a consequence that is particularly relevant to young men who have yet to establish families. The harmful effects of chemotherapy on spermatogenesis are variable, depending on the type and dosage of chemotherapeutic agents used. The current study assessed the effect of cancer therapy on sperm DNA fragmentation by Comet assay. Sperm DNA fragmentation was evaluated in cured cancer patients. The results showed a significant relationship between chemotherapy and double-stranded and single-stranded sperm DNA fragmentation.