Crimean Congo haemorrhagie fever (CCHF) is a viol zoonotic diseases, it is one of the serious communicable diseases with high case 1 fatality. The spectrum of disease presentation ranging from inapparant infection to serious clinical state. Recent reports by WHO showed that the disease is still endemic in Asia (especially East Mediterranean in Region including Iraq and Afghanistan), East Europe especially Kosovo, and in Africa. This comprehensive study is aiming to understand epidemiological aspects of the potential foci in general, especially aspects concerning chain of transmission of the disease and study different social and cultural factors of the inhabitants which affect the chain of transmission of the disease in Iraq. Serological study tools of the disease in human and animals in order to tackle the problem of incriminated possible reservoir and vectors of the disease. This study vas conducted for the period from 1st August 2002 through February 2004 in a disease focus of Nahar El-Emam village, Al-Klialis District, Diyala governorate-Iraq where the case of CCHF was diagnosed. This study is the first complete area study of a focus of the disease in Iraq. A total of 551 persons living in the studied focus from 5 years of age and above among 132 houses. A preceded questionnaire form was used in addition to the interviewed, information gathered including age, sex, occupation, type of families, practice of slaughtering, contact with animals, and type and number of animals. Blood samples were collected from those persons for ELISA test. Regarding farm animals, a total of 270 animals, selected randomly from the same focus including 93 cows, 93 sheep, and 84 goats. Information were gathered regarding types of animals and the number for each family. Samples of blood from these animals were obtained for ELISAtest. As with wild animals, a total of 50 mice (Mus musculus) were trapped from the houses of the same focus, blood samples were obtained for ELISAtest. Regarding the possible vectors of the disease in the focus, a total of 83 ticks were collected from different farm animals in different houses within the same focus. Scientific classification of the ticks regarding their species was done in addition to study of its distribution on the animals. Ticks were not found on human but some persons gave history of contact with them during their life. The results of ELISA test for human sera showed that the prevalence of the positivity among human sera was 6.4%. The positivity was significantly higher among older age group (55-65 years) (P=0.032). There is no significant difference in positivity between male and female. The positivity was significantly higher among butchers (18.5%) than other local inhabitants (5.7%). Regarding the practice of slaughtering, the positivity among those who practice slaughtering (17%) are significantly higher than those not practice slaughtering (5%). While the positivity of the human sera was significantly higher among extended families (53%) than among nuclear families (19%). History of epistaxis or other bleeding showed no significant differences in positivity as most of the persons have an inapparent infection. The positivity among families who had contact with cows (48.4%) was more than the positivity among those families who had contact with sheep (3.2%) and mixed types of animals (32.3%). The results of test of animals' sera by ELISA showed that the positivity rate among cows, sheep, and goats were 33.3%, 33.3%, and 28.5% respectively, with no statistical difference of positivity in between them. All the sera of Mus musculas showed negative results by ELISA I test. The mean reading of positivity among cows sera was 44.92% perperson and was significantly higher than among sheep (32.65%) and goat (17.34%) reflecting the importance of cows in disease transmission than sheep and goats. To predict the infection of any person in the focus, this can be clone by logistic regression equation by; 1-Knowing the number of different types of animals per person, 2-Knowing the mean titer of positivity of the animals present in the focus, 3-Knowing both the number of animals per person and the mean titer of positivity of the animals in the focus. The conelation between the number of different animals per person and the mean titer of positivity of different animals showed a positive correlation of cows per person and mean titer of positi.ity of cows, a positive correlation of cows per person and mean titer of positivity of sheep, a positive correlation of sheep per person and mean titer of positivity of sheep, a positive correlation of sheep per person and mean titer of positivity of goats, a positive correlation of goats per person and mean titer of positivity of sheep, a positive correlation of goats per person and mean titer of positivity of goats. Although the cows are more important in the disease transmission due to Hyalomma species which prefer cows but all these animals are living in the same area and ticks can be transmitted easily in between them especially when they are large number. The results of ticks' classification of species and its distribution on animals showed that Hyalomma species was more than other species found in the focus (76% Vs. 24%). The Hyalomma species distributed on cows was significantly more than other types of farm animals (90% Vs.10%) In conclusion, CCHF virus is endemic in Iraq in an inapparent form of infection, with more positivity among adults especially butchers and those who practice slaughtering reflecting a mode of transmission by direct contact with blood and/or tissues of infected aninmals rather than through ticks, Hyalomma species was the most common species of tick collected and more distributed on cows that plays an important role than : other animals in the disease transmission. From the current study it is recommended that encouragement of surveillance of the disease with periodical screening by using the simple diagnostic methods as ELISA in the focus area, the doctors and medical members should be aware of this health problem, also the population in the focus area need more health education about the disease to protect themselves especially among high risk group (butchers and those with contact with animals) also screening of farm animals from time to time and putting a programme to control the disease among animals with eradication programme for ticks as an important point in restriction of disease transmission.