Abstract In order to determine the prevalence of various disease conditions in the flocks of indigenous and crossbred sheep of small holders in the Central and Southern Sierra of Peru, an examination of carcasses of generally clinically healthy animals was performed during the dry season in five regional slaughterhouses. These post-mortem examinations revealed a high prevalence of parasitism in the respiratory and digestive systems. Approximately 51 % of animals examined had lungworms and associated pneumonic lesions of variable severity. Hydatidosis resulting from Echinococcus granulosis infestation was found in 8.3% of lungs and 6.5% of livers examined. Fasciola hepatica was present in the biliary system of 21% of animals examined and was usually associated with variable degrees of fibrosis. Chronic lung disease due to ovine pulmonary carcinoma was found in 1.7% of sheep examined. The prevalence of this pulmonary tumor in the Criolla and crossbred sheep from the small holder flocks was similar to that reported in the flocks of the region's large cooperative farms that are populated by ‘improved’ breeds of sheep. Thirteen percent of 54 sheep tested had antibodies to ovine lentiviruses, but no lesions of lymphoid interstitial pneumonia were seen.