Patient description: A 17 year old boy complains of vomiting, non-bloody diarrhea, abdominal pain, fever, chills and loss of appetite for the past 3 days. He ate a salad at a restaurant prior to his diarrhea onset. Physical exam was remarkable for pallor, jaundice, and diffuse abdominal tenderness. Lab results were as follows: Hemoglobin: 9.7 g/dL Platelet: 110,000 /cu.mm Creatinine: 3.6 mg/dL blood urea nitrogen (BUN): 73 mg/dL direct bilirubin: 2.4 mg/dL lactate dehydrogenase (LDH): 881 IU/L (normal: 110-265 IU/L) Peripheral blood smear showed a moderate number of schistocytes and helmet cells. Shiga-like toxin-producing E. coli (STEC) stx1/stx2 were found in stools. He has no other underlying disease and he is not on any medications.

Clinical trial eligibility criteria: eligible ages (years): 0.083-18.0,  Atypical Hemolytic-Uremic Syndrome Patient's parent/legal guardian must have been willing and able to give written informed consent and the patient must have been willing to give written informed assent (if applicable as determined by the central IRB/IEC). 2. Pediatric patients with aHUS: Patients could have been newly diagnosed, or with previously diagnosed disease, or post-kidney transplant with the disease. 3. Patients one month to 18 years and body weight ≥ 5kg. 4. Platelet count at screening and baseline visit must have been below lower limit of normal (<LLN). If screening visit and baseline visit are combined into one day, an additional platelet count value obtained at least 24 hours before screening/baseline sample must also be <LLN. 5. Exhibited signs or symptoms of hemolysis at start of current aHUS event (i.e., lactate dehydrogenase (LDH) ≥1.5 x Upper Limit of Normal [ULN] and hemoglobin ≤LLN), fragmented RBC with a negative Coombs test. 6. Serum Creatinine level ≥97 percentile for age at screening (patients requiring dialysis for acute renal failure are also eligible). 7. Patients with aHUS due to complement regulatory protein genetic abnormality or anti-complement factor antibody or those in whom known etiologies of hemolytic uremic syndrome (HUS) have been ruled out as confirmed in the   8. Patients must have been vaccinated against N. meningitidis, pneumococcus and haemophilus (per the vaccine label) at least 14 days prior to study drug initiation or otherwise be protected by prophylactic antibiotics. Patients under age two years were to receive antibiotic prophylaxis throughout the treatment period. 9. Female patients of childbearing potential (female patients who have achieved menarche) must have been practicing an effective, reliable and medically approved contraceptive regimen during the entire duration of the study, including the follow-up period. At the time of the last follow-up visit, patients must have agreed to continue to use adequate contraception methods for up to five months following discontinuation of eculizumab treatment. 10. Able and willing to comply with study procedures Any of the following was regarded as a criterion for from the study: 1. Known familial deficiency (ADAMTS-13 <5%). 2. Shiga toxin E.coli-related hemolytic uremic syndrome (STEC-HUS [known Shiga toxin + E.coli]). 3. History of malignancy within five years of screening. 4. Known human immunodeficiency virus (HIV) infection. 5. Identified drug exposure-related HUS. 6. Infection-related HUS. 7. HUS related to bone marrow transplant (BMT). 8. HUS related to vitamin B12 deficiency. 9. Known Systemic Lupus Erythematosus (SLE) or antiphospholipid antibody positivity or syndrome. 10. Plasma Therapy for >5 weeks prior to enrollment. 11. Chronic dialysis (defined as dialysis on a regular basis as renal replacement therapy for end-stage renal disease [ESRD]). 12. Patients with a confirmed diagnosis of sepsis defined as positive blood cultures within seven days of the screening visit and not treated with antibiotics to which the organism is sensitive. 13. Presence or suspicion of active and untreated systemic bacterial infection that, in the opinion of the Investigator confounds an accurate diagnosis of aHUS or impedes the ability to manage the aHUS disease. 14. Pregnancy or lactation. 15. History of meningococcal/pneumococcal/gonococcal disease. 16. Any medical or psychological condition that, in the opinion of the investigator, could increase the patient's risk by participating in the study or confound the outcome of the study. 17. Patients receiving chronic intravenous immunoglobulin (IVIg) within eight weeks unless for unrelated medical condition (e.g., Hypogammaglobinemia), or chronic Rituximab therapy within 12 weeks of the screening visit. 18. Patients receiving other immunosuppressive therapies such as steroids, mTOR inhibitors, calcineurin inhibitors (e.g., cyclosporine or tacrolimus are excluded unless: [1] part of an established post-transplant anti-rejection regime, or [2] patient has confirmed anti-Complement Factor antibodies antibody requiring immunosuppressive therapy or [3] steroids are being used for a condition other than aHUS (example asthma). 19. Participation in any other investigational drug trial or device trial, or procedures beginning four weeks prior to screening and throughout the entire trial 20. Prior use of eculizumab, hypersensitivity to eculizumab, to murine proteins or to one of the excipients