Background Atypical haemolytic uraemic syndrome (aHUS) is a rare, life-threatening, chronic thrombotic microangiopathy (TMA) caused by uncontrolled complement dysregulation. Eculizumab, a humanised anti-C5 monoclonal antibody, is the only approved treatment of aHUS. Purpose To assess the effectiveness and safety of eculizumab in patients with aHUS and/or TMA. Material and methods A retrospective observational study was conducted from June 2012 to September 2015 in a general university hospital, including patients diagnosed with aHUS and/or TMA. All patients received an induction period of 900 mg eculizumab weekly (weeks 1–4) followed by a maintenance period of 1200 mg in week 5 and then 1200 mg every 2 weeks. Demographic (sex and age) and clinical data (platelet count, haemoglobin, lactate dehydrogenase (LDH), haptoglobin and renal function) were systematically collected at baseline and during treatment. Effectiveness was assessed by complete response (normalisation of haematologic parameters combined with an improvement in renal function), haematologic response (normalisation of platelet count and LDH) and TMA event free status (no decrease in platelet count of >25%, no plasma exchange (PE) and no dialysis). Adverse events were registered. Results Six patients were included: 4 men, aged 34 ± 7years, 4 diagnosed with aHUS and 2 with post-transplant TMA. Five patients received PE and dialysis prior to eculizumab treatment. Clinical data at baseline were: platelet count (138 ± 65×10 9 /L), haemoglobin (8.8 ± 1.0 g/dL), LDH (320.3 ± 269.2UI/L), haptoglobin (47.3 ± 38.5 mg/dL) and creatinine (6.3 ± 2.8 mg/dL). After the induction period, complete response was achieved in 3/6 patients, haematologic response in 4/6 patients and TMA event free status in 5/6 patients. Treatment response was maintained in all patients during the follow-up period (median 33 weeks; min 7, max 156). There were no adverse events. Conclusion Eculizumab showed effectiveness and safety profiles consistent with those seen in previous clinical trials, showing that it is a well tolerated and effective drug in patients with aHUS and post-transplant TMA. References and/or Acknowledgements Legendre CM, Licht C, Muus P, et al . Terminal complement inhibitor eculizumab in atypical hemolytic-uremic syndrome. N Engl J Med 2013;368:2169–81 No conflict of interest.