Abstract: The ultrastructure of hydatid cysts extirpated from the lungs of three cases with E. granulosus infection was observed and illustrated by scanning and transmission electron microscopy. SEM showed that vesicles were different in size and shape, either round or elliptic, covered with thin and thick filaments on the germinal layer and on the lateral side of the laminated layer. Regular-edged, crack-shaped pits were found at different distances on the germinal layer. TEM showed numerous long and thick microvilli arranged regularly on the germinal layer. Each microvillus appears to be a four-layered membraneous structure. A number of vesicles and microtubules with less filaments are seen in the compact band beneath the microvilli. Within the cytoplasm there are prominent mitochondria, rough endoplasmic reticulum, ribosomes, Golgi bodies, smooth muscle and two kinds of protoplasts of different morphological structures.