The study was carried out to determine the prevalence of hydatidosis among the sheep carcasses at Al-Ahsa region, Saudi Arabia. The study included also histopathological tissue evaluation. The results of the present study showed that the prevalence of hydatidosis among sheep carcasses was 6.60 % (98/1485); meanwhile among the native sheep breed was 7.70 %, and 5.8 % among the imported ones. Concerning the effect of age, the prevalence of hydatidosis increased significantly (p≤ 0.0001) in old aged sheep. On the other hand, the prevalence in liver, lung, heart and muscles was 66.3%, 23.4%, 7.1% and 3.0%, respectively. Regarding the cyst state in sheep, the percentages of viable, non-viable, sterile and calcified one were 24.4 %, 12.2 %, 7.14 % and 56.1 %, respectively. Meanwhile, results of histopathological examination had shown that most of hydatid cysts in sheep were fertile
Key words: Hydatid cyst, Sheep, Prevalence, Histopathology, Saudi Arabia.