Invasive fungal infections are a problem of both, modern medicine and haematology and this is especially true in the case of immunocompromised patient. The reason for this is that in recent years a large number of patients are treated by bone marrow transplantation, consequently, they become immunocompromised, and thus there is a high risk of mortality and morbidity due to fungal infections. It is extremely important to make a timely diagnosis in such patients because the result of the treatment depends on it. If the diagnosis is not made in time, the lethal outcome of such a patient is possible. All organs and organ systems can be affected by fungal pathogens. Antifungal drugs have a major role in the treatment of immunocompromised patients suffering from fungal infections. There is a number of antifungals available on the market in recent years and some of them have minimal side effects. The choice of antifungal drug for the treatment of infected patient depends on his general condition, laboratory findings and the type of fungal infection suspected or proven, as well as on the attitude and preference of the clinician treating him. Except for the treatment of pre-existing fungal infections, antifungal drugs are also used prophylactically with the aim to prevent infections caused by fungi. I addition to antifungal drugs, air purification is also used in the prevention of fungal infections, via HEPA filters, in vulnerable groups of patients, special food preparation and rigorous disinfection of patients rooms. Patients receiving antifungal drugs belong to the group of high risk haematological patients: patients with acute leukaemia and prolonged neutropenia and patients after allogeneic hematopoietic stem cell transplantation.