We present a case of hemophagocytosis during infection with the intraërythrocytic protozoan Babesia microti in a 47-year-old splenectomized renal allograft recipient. After therapy with clindamycin and quinine a relapse responded to atovaquone; durable remission was not achieved until trimethoprim/sulfa was added. We postulate the severity of our patient's syndrome was due to splenectomy and chronic immunosuppression. Babesiosis should be considered when immunocompromised patients develop pancytopenia.