Ions with energy greater than 40 eV have been measured on the nightside of Venus by the Pioneer Venus orbiter neutral mass spectrometer (ONMS). For periapsis altitudes beyond 1500 km they are confined to solar zenith angles greater than 120¿. The nightside energetic ion composition at 2000 km resembles the nightside thermal ion composition occuring at 1000 km with the dominant species being O+. Postflight laboratory calibrations performed on the ONMS backup unit have been used to estimate the energetic O+ ambient flux and density. The direction from which the energetic ions appear to be coming can be determined because the ONMS is mounted at an angle with respect to the spin axis of the spacecraft. Both tailward and antitailward components of the apparent ion flow is observed perpendicular to the ecliptic plane.