A white girl presented at 8 months of age with thrombotic microangiopathy, followed by recurrent episodes of renal dysfunction, hemolysis, and thrombocytopenia, compatible with atypical hemolytic uremic syndrome. The episodes of the syndrome were treated by a combination of infusions of fresh frozen plasma, plasmapheresis, and continuous venovenous hemodialysis. Interval resolution occurred between episodes. At 2 years of age, prophylactic infusions of fresh frozen plasma were started between relapses, but this proved to be poorly protective; however, introduction of prophylactic intravenous gamma globulin at age 3.5 years resulted in prolonged remission (42 months). Serum levels of the third and fourth components of complement, total hemolytic complement, and complement factor H were normal. Results of the third component functional assay were low before and normalized after the start of immunoglobulin G prophylaxis. A missense mutation of complement factor H was identified. At 6 years of age, the patient underwent bilateral native nephrectomy and started long-term peritoneal dialysis, followed by a combined liver-kidney transplant at age 8 years. Four and a half years after transplant, she has excellent renal and liver graft function without recurrence of atypical hemolytic uremic syndrome.