Abstract
Cystoisosporiasis is caused by a coccidian parasite that is found worldwide and can cause diarrheal illness. It is more common in the immunocompromised, in whom it can cause extended and severe disease courses. Diagnosis is not always straightforward as oocytes are not always present in routine stool samples, but it is possible to visualize the organism with specialized staining techniques as well as within enterocytes on intestinal biopsies. We present a case in which this mode of diagnosis was crucial for determining the cause of diarrhea in a patient with HIV and CD4 count above 200 cells/mm(3).