We report preliminary findings on drill population ecology, feeding ecology, primate associations and conservation status in Korup National Park, Cameroon, based on analysis of data collected during 1,346 km (620 field hours) of trail patrols from February to June 2006. We encountered drills on 25 occasions and collected 304 fecal samples. Group size was estimated on four occasions (> or =25, > or =40, > or =67, > or =77), and multiple males were heard emitting the characteristic two-phase grunt of mature male drills in two of these groups. We saw a solitary male drill once. Examination of fecal samples indicated a seasonally variable diet consisting mainly of seeds, fruit pith, leaves and insects (especially ants and termites). Irvingia gabonensis and Musanga cecropioides fruits showed the highest percentage of occurrence in May (96%) and March (75%) samples, respectively, and could be a major food source for drills at that time. Drills were in association with at least one additional primate species during 57.9% of observations. These associations involved all of the diurnal primates found in Korup (Cercopithecus mona, Cercopithecus nictitans, Cercopithecus erythrotis, Cercopithecus pogonias, Piliocolobus preussi and Cercocebus torquatus) except chimpanzees (Pan troglodytes). We discuss our findings in terms of existing knowledge about drill ecology and highlight the urgent need for the protection of the significant drill population in Korup National Park.