Introduction: High flow nasal cannula is commonly known therapeutic option of the treatment of acute respiratory failure during a course of COVID-19 and other lung disorders. Together with non-invasive ventilation it states a bridging therapy before an introduction of invasive respiratory support and often allows to avoid the latter. High flow nasal cannula features a favourable safety profile. However, the following case report purpose is to draw attention to a rare but potentially fatal complication of the aforementioned therapeutic method. Case report: The paper describes a 63-years old white male admitted to the infectious diseases ward in April 2021 due to the critically severe course of COVID-19 with an involvement of 90% lung tissue as it had been shown on computed tomography scans. From the beginning the patient underwent high flow nasal cannula. After 3 days of the treatment, he developed massive nasal haemorrhage. Despite an immediate anterior tamponade epistaxis led to a rapid respiratory deterioration, which caused necessity of an intubation and invasive ventilation. Cardiac arrest with pulseless electrical activity occurred in spite of measures taken. Discussion: The patient died after an unsuccessful resuscitation. The risk of epistaxis, which can result in a critical deterioration of patient’s respiratory capacity, must be taken into account when high flow nasal cannula is implemented. Conclusions: In view of increasing popularity of the discussed therapeutic method there is an urgent need of cohort studies in order to assess risk factors and proper preventive measures regarding epistaxis resulting from a usage of high flow nasal cannula.