Detvction & determination of prevalence of lesions in slaughtered sheep is the first step in planning of prevention of economical lossus. in this study, 1627 sheep carasses were inspected in lavasan slaughter house (Tehran province) at 13 times on the summer
1997. carcasses lesions were observed at 336 of them. Species and frequency of lesions were analyzed by gender, age and breed. The ratio of parasitic lesions was more than others (76%) but prevalence of liver hydatid cysts, liver worms, Dicroceliosis and Cistisercosts were 5.84% (CI = 4.7% = 6.98%), 3.69% (CI = 2.77%-4.61%),2.52%(1.76% 3.28%),2.5%(1.15%2.85%)
respectively. Prevalence of non parasitical lesions were less than 1% . Prevalence of Hydatid Cyst was significantly higher than the other parasitic ones (0.01 <0.05). Caseuse lymphodenitis also was more prevalent than the others 1.7 % m (CI = 0.65 Yo 1.69%) and the prevalence of non parasitic lesions was less than 1%. The Proportion of non parasitic lesions was less than 1%. The Proportion of infestation of carcasses in females was more than males sheep with the exception of Hydatid cyst parasitic infestation which was observed in lambs of 6 months of age or less. Native and Afshan breeds had more lesions of Ghoochani breed. Hydatid Cyst was observed in all examined breeds (in comparison of the other lesions. this study from the epidemiological point of view could support further surveilance of related diseases in this region.