A 29-year-old woman presented with bloody diarrhea, abdominal pain, hemolytic anemia, thrombocytopenia, and acute renal failure. She was diagnosed with Escherichia coli O104:H4-associated hemolytic-uremic syndrome (HUS) and treated with plasmapheresis and hemodialysis for 3 weeks. She recovered without sequelae. To the best of our knowledge, this is the first report of Escherichia coli O104:H4-associated HUS in Korea. We recommend that Escherichia coli O104:H4, as well as the more common O157:H7, be considered in the diagnosis of bloody diarrhea-associated HUS.