The morphology of the outer face of the eggshell, its appearance in cross fractures and the surface morphology of the inner face are described in the green stink bug Acrosternum (Chinavia) marginatum (Hemiptera: Pentatomidae) using scanning electron microscopy. Deposited eggs are barrel-shaped and the surface consists of hexagonally arranged, funnel-shaped pits that possess transverse diaphragms in their slender, basal portions. Only minor differences are detectable between the central portion of the anterior plate (the operculum) and the lateral wall together with the basal portion of the eggshell. The rim at the anterior pole of the egg carries processes with a bulbous end, the aero-micropylar processes. A narrow band of the anterior plate bordering these processes shows hexagonally arranged elements. These differ from those of the operculum and the lateral wall, in that cylindrical pits are abundant. During hatching, the operculum is lifted precisely at the rim of this area. Inspection of the periphery of the inner face of the operculum reveals slender, radially arranged grooves. Their arrangement and spacing indicate that they bear a spatial relationship with the aero-micropylar processes. Their role may lie in guiding the sperm to the site where fertilization occurs and in facilitating the gas exchange of the embryo. The remainder of the eggshell carries shallow elevations at its inner face. Exterior and interior features of the eggshell, as well as its appearance in cross-fractures, are discussed.