Leukemias are malignant diseases of the bone marrow. We distinguish four main types: acute lymphocytic (ALL), acute myeloid (AML), chronic lymphocytic (CLL) and chronic myeloid leukemia (CML), which differ clinically and biologically in many ways. Risk factors for these diseases are associated with some genetic diseases and exposure to radiation and chemicals, but in most cases the true cause of leukemia remains unknown. The symptoms of leukemia occur as a result of insufficient function of the bone marrow occupied by diseased cells. The most common symptoms are: general weakness (due to the development of anemia), tendency to bleed (due to low platelet count), fever and frequent infections (due to weakened immune function), bone pain, weight loss. The diagnosis is made on the basis of blood counts (leukocyte count is usually elevated), bone marrow examination (hip or sternum aspiration puncture to obtain a bone marrow sample in which in which microscope determines the presence of multiplied leukemia cells) and special laboratory methods used to classify the type of disease . Physical examination can sometimes show enlarged lymph nodes, spleen and liver, signs of bleeding, pale skin. Acute leukemias are rapidly progressing and aggressive and should be treated as soon as possible. AL are most commonly curable in children while a lower cure rate is recorded in the adult population. The chances of recovery have greatly increased thanks to transplant treatment. Unlike acute, chronic lymphocytic leukemia is not aggressive in most cases. They most often affect the elderly (> 65 years), and children very rarely. In patients with CLL, some need only disease control, others are treated only after a few years due to disease progression, and in some, treatment is carried out from the moment of diagnosis due to the presence of a large tumor mass. Treatment is pierced by immunotherapy, chemotherapy, and stem cell transplantation. An important feature of CML is the existence of the so-called Philadelphia chromosome (translocation between chromosomes 9 and 22) which is the culprit for unbridled cell proliferation. The disease usually develops into AL after a few years and then the only treatment is stem cell transplantation. Recently, great progress has been made in the treatment with smart drugs, however, not every patient has a predisposition to receive this type of therapy. Leukemias can be seriously lifethreatening, so timely diagnosis, appropriate choice of treatment and quality health care are prerequisites for a positive outcome of the disease.