Head and neck cancers (head and neck squamous cell carcinomas [HNSCC]) are a heterogeneous group of neoplasms with varying presenting symptoms, treatment, and expected outcome. There is a need to find an effective way of its treatment at the molecular level. Thus, we should identify the mechanism of cancer cell response to damaging agents' activity, especially at DNA level. Our major goal was to evaluate the efficacy of DNA double strand breaks (DSBs) repair in HTB-43 and SCC-25 cancer cell lines as well as lymphocytes taken from HNSCC patients and healthy donors. The DNA repair efficiency was measured by neutral comet assay as well as extrachromosomal assay for DNA DSBs repair (TAK assay). We determined the levels of two main pathways of DNA DSBs-nonhomologous end joining (NHEJ) and homologous recombination repair (HRR). Neutral comet assay was used for evaluation of DNA DSBs repair after treatment with genotoxic agents. DNA DSBs induced by gamma radiation were repaired slower in lymphocytes from HNSCC patients than in lymphocytes from healthy controls. HTB-43 and SCC-25 cancer cell lines have higher efficacy of NHEJ and HRR than lymphocytes taken from patients as well as control subjects. Our results confirm the necessity of further studies on the mechanisms of DNA DSBs repair to provide insight into the molecular basis of head and neck cancer, which will allow us to improve methods of HNSCC treatment.