Rapid expansion of HIV/AIDS pandemic has brought about a dramatic change in the fauna ofrnintestinal parasites worldwide. In HIV/AIDS patients, opportunistic intestinal parasites (OIP)rnare seriously causing hard- to-control diarrhoea in Africa. The well-known OIP that causerndiarrhoea at latest stage of HIV infection are Cryptosporidium parvum, Isospora belli,rnEnterocytozoon bieneusi, Encephalitozoon intestinals and Cyclospora cayetenesis. Therndetermination and recognition of these newly emerging parasites in immunocompetent,rnimmunocompromised and HIV/AIDS patients was facilitated and increased with the advent ofrnnewly improved diagnostic methods. However, no detailed investigation of these parasitesrnexists in Ethiopia. HIV/AIDS is also one of the major public health problems in Ethiopiarnseverely affecting the productive and reproductive age groups of the society. The presentrnstudy was aimed at investigating the relationship of OIP and HIV/AIDS in diarrhoea patientsrnin Ethiopia . The assessment of the chemotherapeutic effect of intestinal parasites in thernWonji HIV/AIDS natural history study cohort showed that follow up visits of the cohortrnpopulation based on scheduled regular visit diagnosis and treatment resulted in an impressivernsustainable control of intestinal parasitic infections as compared to patients that visited Wonjirnhospital without such follow up. The Hospital setting was found more appropriate to study thernrelationship of intestinal parasites with emphasis on OIP in diarrhoeal patients withrnHIV/AIDS. After informed consent was obtained, 330 diarrhoeal patients were recruited.rnClinical data and biological samples were collected. Blood was processed for HIV-testing byrnusing ELISA and reactive samples were confirmed by western blot. CD4+cell count was donernby FACScan, and viral load by NASBA. Stool was processed for parasites including ova, byrndirect and formol-ether method, Modified Ziehl Neelsen for Crypotosporidium, Isospora andrnxviiirnCyclospora, Autofluorecence for Cyclospora and Flurochrome Uvtitex-2B and nested PCRrnfor intestinal microsporidia. Out of 330 diarrhoeal patients examined for intestinal parasitesrn268(81.2%) were positive for one or more parasites; and of these 74.2% were HIV positive.rnThe major clinical presentations such as chronic diarrhoea lasted > 4weeks, severe weightrnloss>10%, and anorexia were more common in HIV positive than HIV negative patients. Therncommon intestinal parasites such as Ascaris lumbricoides, Trichuris trichiura, Hookwormrnspp. and Schistosoma mansoni were very rare, and for each one of them the prevalence wasrnbelow 2% in the HIV positives, and relatively high in the HIV negatives. Over all the nonopportunisticrnintestinal parasites such as A. lumbricoides, Taenia Spp. andrnE.histolytica/dispar were significantly higher in HIV negatives than HIV positives (P