Isosporiasis is a gastrointestinal parasitic disease with clinical manifestations ranging from asymptomatic to severe diarrhea and dehydration. It is not a well-known disease, and it is rarely reported because it is difficult to recognize in the stool. However, in every place where there has been systematic research, this disease has been found. Isosporiasis is currently of note because it is a secondary infection of HIV/AIDS and the Centers for Disease Control and Prevention considers it an AIDS-defining condition. There are medications for the disease.