BACKGROUND A rhesus macaque developed chronic anemia, lymphocytic leukocytopenia, fever, and anorexia while immunodeficient following inoculation with a simian-human immunodeficiency virus. METHODS A complete blood count, peripheral blood smear, polymerase chain reaction and gene sequence were performed. RESULTS Blood smears demonstrated persistent intraerythrocytic piroplasms with rare Maltese cross forms. Babesia microti-like protozoa were confirmed by polymerase chain reaction and sequencing of the 18S ribosomal RNA gene. CONCLUSION With continued use of non-human primates as models for human diseases, infection and complications from babesiosis should be monitored.