The experimental electron density of ethylene oxide was derived from a multipole refinement of 100 K X-ray data and complemented by density-functional calculations at experimental and optimized geometry. Atomic and bond-topological properties were derived using the atoms-in-molecules (AIM) formalism. The high strain in the three-membered ring molecule is mainly expressed by the high ellipticities of the three bonds in this ring, while the bond paths are only slightly bent for the C-C bond, but are virtually straight for the C-O bond.