Alveolar echinococcosis (AE), which is caused by ingestion of eggs of the fox tapeworm Echinococcus multilocularis,is the most potentially lethal parasitic infection because of its tendency to invade and proliferatein the liver and the difficulty in treatment. This article describes a case of alveolar echinococcosis found inAteles geoffroyi in Mashhad, Iran. The cysts were characterized as an alveolar structure, composed of numeroussmall vesicles in liver, abdominal cavity, retroperitoneum and lungs. A characteristic feature of thesevesicles was its exogenous tumor-like proliferation. These cysts were filled with numerous protoscolecessuggesting a potential role of this monkey in cycle of transmission. Up to now, this is probably the first reportof alveolar echinococcosis in A. geoffroyi in the world.

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