Background & Objectives: Cryptosporidium is a coccidial protozoa parasite belonging to subphylum of Apicomplexa. Although it is globally widespread and its species exist all over the world, this parasite was unknown until several years ago. Nowadays it is considered as an important infective agent in Immunocompromised hosts especially patients with AIDS. Due to high mortality rate of this infection in immunocompromised and cancerous patients and because of the popularity of Urmia as one of the animal husbandry regions in Iran and since this disease is likely to transfer from animals to human beings this study was conducted to determine the rate of contamination with this parasite.

 Methods: This case-control study was performed on 72 children (case) with cancer who referred to oncology clinic of Urmia Imam Hospital during 2001. Another 30 children with normal immune system were selected as controls. To determine the amount of contamination with parasite, two fecal specimens were collected from each patient. After being concentrated with Formalin–Ether, these specimens were examined using modified acid fast method.

 Results: Three cases of�cryptosporidiosis was seen in the patients (4.16%). Of these, there were 2 patients from the rural area and 1 from urban region. There was no significant relationship between the presence of cryptosporidiosis and living in rural or urban areas.

 Conclusion: Cryptosporidium was detected in three cases of the patients under study who were undertaking chemotherapy. However since the population under study was small, no statistically significant relationship was found between being immunocompromised and contamination with parasite.