An abattoir survey of 212 sheep of different ages was undertaken to determine the local epidemiological transmission patterns of Echinococcus granulosus in the central Peruvian Andes. Overall prevalence of the disease in sheep in this survey (which ended in July 1996) was 77·4%, with 96% of sheep aged ≥6 years being infected. Of 1165 cysts examined, 41·1% were fertile with a mean protoscolex viability of 73·2%. A logistic regression model for the distribution of cyst fertility and type by age, location and size is described. Mathematical modelling also determined that infection pressure on sheep was 0·44 infections per year and that the mean number of cysts increased linearly by 1·28 cysts per year. These data suggest that E. granulosus is in an endemic state in this area and control measures could drive the disease towards extinction.