A liver, heart, iliac vessel and two kidneys were recovered from a 39-year-old man who died of traumatic head injury and were transplanted into five recipients. The liver recipient 18 days posttransplantation presented with headache, ataxia and fever, followed by rapid neurologic decline and death. Diagnosis of granulomatous amebic encephalitis was made on autopsy. Balamuthia mandrillaris infection was confirmed with immunohistochemical and polymerase chain reaction (PCR) assays. Donor and recipients' sera were tested for B. mandrillaris antibodies. Donor brain was negative for Balamuthia by immunohistochemistry and PCR; donor serum Balamuthia antibody titer was positive (1:64). Antibody titers in all recipients were positive (range, 1:64-1:512). Recipients received a four- to five-drug combination of miltefosine or pentamidine, azithromycin, albendazole, sulfadiazine and fluconazole. Nausea, vomiting, elevated liver transaminases and renal insufficiency were common. All other recipients survived and have remained asymptomatic 24 months posttransplant. This is the third donor-derived Balamuthia infection cluster described in solid organ transplant recipients in the United States. As Balamuthia serologic testing is only available through a national reference laboratory, it is not feasible for donor screening, but may be useful to determine exposure status in recipients and to help guide chemotherapy. This study describes the investigation of a donor-derived Balamuthia infection cluster in solid organ transplant recipients in the United States, and the usefulness of Balamuthia serologic testing to determine exposure status and guide prophylaxis in recipients. © Copyright 2014 The American Society of Transplantation and the American Society of Transplant Surgeons.