An epidemiological clinical and pathological stud of aedi-Visna virus (MVV) infection inrnsheep vas carried out in highland areas of the Amhara ational Regional State (ANRS). Thernpurpose of the stud as to estimate the pre alence and distribution of the disease andrnidenti associated risk factors vith the occurrence of the disease. A total of 2417 serumrnsamples vere collected from smallholder farms (n = 1491 and sheep breeding ranches (n =rn926) from ~oyember 2003 to February 200 . Indirect-Enzyme Linked Immunosorbent Assarni-ELISA) and Agar Gel Immunodiffusion (AGID) tests were employed to determine thernpresence of antibodies against infection. All sheep sampled vere clinically investigatedrn,here as fe seropositive sheep ' ere slaughtered and examined for gross lesions andrnhistopathological pictures.rnThe apparent seropre alence of infection was found to be different between thernmanagement types; 6.6% (95% CI = 5.4 - 7.9) in smallholder farms and 30% (950/0 CI = 27.1rn- 33.1) in sheep ranches. The difference in pre alence between the two sheep managementrntypes among ranche~ and eredas was statistically significant (P < 0.001). The prevalence ofrninfection increased 'th increasing flock size and found to be higher in ranches (82.6%rnthan in the smallholder farms 18.8% . The breed related seropre alence aried from 16% inrnindigenous sheep to .6% in Awassi sheep. The age-specific seropre alence increased withrnthe age of sheep from 2.8% in yearlings to 6.5% at 7 years old. F10ck size, breed, age andrncontact v. ith ranch sheep were significant (p < 0.0001) risk factors associated with therno curren e and transmission of infection.rnIn clinical disease in estigatio~ 31 out of 3 8.3%) seroposi ti e sheep were found tornexpress the clinical disease. Among the seropositi es with 0 ert clinical disease, 96.8% erernfrom sheep ranches "hile 3 .2% from smallholder farms. There as statistically significant Â¥rn8.3' d.f = l ' P < 0.001 association bemeen the clinical disease and thernseropositivi . The clinical disease increased vith age of animals. The large proportion of thernclinical disease in ranches and older animals as associated ,vith the flock management andrnhigh Ie el of infection.rnThe clinical disease ,vas significantl different among sheep breeds (P