Background & Objectives: Cryptosporidium is an intracellular – extracytoplasmic parasite that has taken much attention in last 20 years as a clinically important human pathogen. Cryptosporidial infection can be transmitted from fecally contaminated food or water and from animal-human or human-human contact. In immunocompromised persons, the illness is much more severe such as debilitation, fatigue, cholera-like diarrhea, severe abdominal cramps, low-grade fever, severe weight loss and Anorexia. Because there was no regional study about cryptosporidiosis in Ardabil, we carried out this survey to determine the prevalence of cryptosporidiosis among the children hospitalized in Ardabil.

 Methods: This descriptive and analytical study was carried out on 371 patients in Sabalab and Aliasghar hospitals of Ardabil between 2004 and 2005. A questionnaire was filled for each patient. Stool samples were examined by concentrated formal - ether method and stained with modified Ziehl-Neelson method. The data were analyzed with SPSS (ver 11) using Chi-square test.

  Results: We analyzed 371 stool samples from children with diarrhea. Cryptosporidium oocysts were detected microscopically in 15 samples. Its prevalence was 4.04% in infected patients. 66.7% of the infected ones were at the age of 6 to 24 months, 20% 25-48 months, and 13.3% 49-72 months.

 Condusion: Because cryptosporidiosis was more prevalent at the age of 6-24 months, health education is more necessary for their mothers.