A patient with aHUS. The patient is a 45-year-old woman with a longstanding history of untreated hypertension who presented to primary care for foot and ankle swelling and was found to have a blood pressure of 184/102 and a creatinine of 7.2 (636 mmol/L). Her C3 level was one-third of normal, the lactic acid dehydrogenase was elevated, the haptoglobin was decreased, and the platelet count was in the normal range. The initial diagnosis of TTP was entertained. The patient achieved some degree of renal recovery with the start of PE. She received 6 doses of PE peri-presentation, but then discontinued it because of self-reported unacceptable side effects. The patient declined to start eculizumab and was subsequently lost to follow-up. Upon re-presentation 6 months later, she required dialysis and was started on eculizumab. Seven months after re-presentation, the patient remains on dialysis and genetic studies demonstrated a mutation in C3. A corresponding color normal bar has been added to each graph. This case highlights several interesting aspects of aHUS: the platelet count does not have to be below 150 000 K/mm², the diagnosis of aHUS can be delayed by the consideration of alternate TMA-causing disease; patients may present with late-stage renal disease; plasma exchange can be effective, but may be difficult for patients to sustain; a late start of anticomplement therapy can recover the hematologic findings of aHUS, but may not facilitate renal recovery; genetic testing cannot be part of the acute management; and C3 levels may remain low even when hematologic remission is achieved.