The use of Bt maize could directly or indirectly affect non-target organisms.  Assessment of the impacts of Bt crops is hampered by the lack of even the most basic checklist of the species present in most systems.  In South Africa the maize agroecosystem is of particular interest because of the large area planted with Bt maize (Event MON810) for the control of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) populations.  The aims of this study were to determine the diversity of Lepidoptera species that feed on or are closely associated with maize, and to assess the possible effects of Bt maize on the incidence of Lepidoptera damage under field conditions.  Field surveys were conducted at 24 sites during the 2004/2005 and 2005/2006 cropping seasons.  Fifteen species of Lepidoptera were recorded on maize.  Six of these species were recorded to feed on Bt maize.  Limited information is available on host plants and biology of some of these species.  The incidences of Lepidoptera-infested plants and infestation levels were generally lower in Bt fields than in non-Bt fields possibly indicating that these species may be affected by Bt maize.  Results showed that B. fusca larvae were able to survive on Bt maize at low population levels.  On the basis of exposure and risk of resistance development, Helicoverpa armigera and Acantholeucania loreyi can be considered to be important non-target lepidopteran herbivores on maize in South Africa.