C. belli is a protozoan pathogen that causes an opportunistic infection primarily in immunocompromised patients with AIDS and/or ATL.[8] Cystoisosporiasis is also reported in patients with non-Hodgkin lymphoma, alcoholism, and ulcerative colitis taking azathioprine and anti-TNF-α antibody treatment.[9–11] However, only a few reports described C. belli infection in immunocompetent individuals.[12,13] In our case, there was no evidence of immunocompromised status by extensive examinations. Here, TNF is linked to AIDS.