We studied how mammals used a wildlife overpass across a motorway in central Netherlands using track counts in 1989, 1994 and 1995. Throughout the study the overpass was used most frequently by red deer (Cervus elaphus) and wild boar (Sus scrofa) and, less often, by roe deer (Capreolus capreolus), red fox (Vulpes vulpes), fallow deer (Dama dama), Highland cattle, and badger (Meles meles). For red deer and wild boar the highest incidence of use was in autumn/early winter, correlating with the rutting season. Small mammals caught on the overpass were wood mouse (Apodemus sylvaticus), common vole (Microtus arvalis) and common shrew (Sorex araneus). The wildlife overpasses can be an effective means of connecting habitats for a wide range of mammals but the effectiveness is related to the width of the overpass. For large mammals a minimum width of 40-50 meters is recommended.