Hypoxia, which could be defined as the level of oxygen tension in the body that is below the normal physiological value, is a process that is often observed in several diseases and occurs in most malignant tumors. On the other hand, in hypoxia several pathological conditions could occur, which could be caused by external and internal factors. During carcinogenesis, hypoxia may promote metastasis and an unfavorable prognosis. When infected with COVID-19, there is a «silent hypoxia», which could asymptomatically destroy the body. The review is devoted to hypoxia’s role in the development of some pathological conditions and malignant tumors.