Atypical hemolytic – uremic syndrome (aHUS) is a rare disease from thrombotic microangiopathies group. It is clinicali presented as a characteristic trias of symptoms: microangiopathic hemolytic anemia, thrombocytopenia and renal impairment. With recent advances in genetics and imunology, aHUS has been associeted with defects of alternative pathway of complement, mostly in regulatory proteins such as complement factor H, complement factor I, etc. Except defects of complement system, there are different triggers associated with development of aHUS. Depending of the etiopathogenic background of the illness there are differencies in clinical presentation. Some genetic dissorders are prone to faster progression of kidney failure. Kidney transplantation is the therapy of choice in patients with kidney failure, but patients with aHUS often have relapses of primary disease and graft rejection. When eculizumab was introduced it stared to present new therapeutic posibility. Eculizumab is a monoclonal antibody aginst C5 component of coplement. It prevents finishing of a complement cascade and further damaging of kidne tissue. A case of aHUS with confirmed mutations was noted in the Hospital University Center Zagreb.