Introduction:
Hemolytic uremic syndrome (HUS) is a complex of symptoms with heterogeneous etiology, constituting the most common cause of acute kidney injury (AKI) in children below 4 years of age. Although there are simple diagnostic criteria, in clinical practice difficulties are observed, usually associated with the determination of HUS cause.

Material and Methods:
The study presents the course of diagnosis and treatment of three children with pre-established clinical diagnosis of HUS. The first patient was admitted to hospital at the age of 5 months, when he presented the “classic” HUS symptoms preceded by an episode of acute diarrhea. After successful treatment of the first episode, in the next 30 months, 6 relapses of the “active” phase of HUS were observed, combining the features of HUS and nephrotic syndrome. The introduction of prophylactic plasma infusions currently enables maintaining the boy in the remission phase. The second child was sent to hospital at the age of 3 months because of a triad of symptoms typical of HUS. The ultimate explanation for the observed abnormalities proved extensive retroperitoneal vascular malformation with secondary activation of intravascular coagulation. The third patient was a 2.5-year-old boy, who manifested mild symptoms of HUS. Family history was remarkable (the death of his brother because of extremely severe HUS of persistent, relapsing course). A complete remission of the symptoms was obtained by repeated plasma infusions treatment.

Conclusions:
In the case of coexistence of hemolytic anemia, thrombocytopenia and AKI, it is necessary to take into account also the other causes than HUS. Differentiation of the mechanisms leading to the development of HUS translates into a wide range of treatment modalities in this group of patients. Properly selected therapies offer the opportunity for a quick remission free of severe complications.