Neonatal calf diarrhea due to cryptosporidium is a major health problem. It causes extensive economic losses. This study was carried out on newborn calves in different parts of east Azarbayjan province over November 2001 - 2002. Five hundred feacal samples were taken from diarrheic calves under the age of 2 months from 25 commercial dairies and referral cases to the private clinics in four districts of Azarbayjan province. Samples were fixed in the formalin and then stained by modified Ziehl-Neelsen procedure in Department of Parasitology, Faculty of Medicine, Tabriz University of Medical Sciences. Data were statistically analyzed using Chi-square test. The positive samples for cryptosporidium were confirmed as 41.4% (207 samples out of 500) cases and a significant difference was found between the prevalence rate in relation to the seasons of study (p<0.05). While the highest prevalency was in summer (49.6%), the least rate was in the winter (30.4%). Statistical significance was also found between the age groups regarding the prevalence rate in infected calves (p<0.05), mostly at 6 to 8 weeks of age (61.4%) and less on one week of age (25.21%). There was not any significant difference between different districts according the prevalence rate of infection. The severity of infection was found 30.43% (+), 34.3% (++) and 35.26% (+++) respectively. Meanwhile, positive association between the severity of infection and diarrhea was also shown.