The crested black macaque Macaca nigra, endemic to Sulawesi, Indonesia, is categorized as Critically Endangered on the IUCN Red List and its population in the Tangkoko Nature Reserve is probably the only viable one within its native range. Earlier studies suggested that this population suffered a decline of 75% during 1978–1994. To evaluate its current status we conducted a line transect survey in the Reserve and assessed effects of ecological and anthropogenic variables on macaque abundance and distribution. We estimated a density of 44.9 individuals km-2 (95% confidence interval, CI, 25.6–78.8) and a total population of 1,951 individuals (CI 1,113–3,421). This estimate of density is 35% lower than that of 68.7 individuals km-2 in 1994. There were moderate to strong correlations between macaque abundance and vegetation structure (basal area and canopy tree density). We observed illegal logging in the area and therefore habitat quality for macaques may be indirectly affected by illegal human activities. If our population estimate is projected linearly M. nigra could become extinct in Tangkoko within 46 years, highlighting the urgent need to improve management of illegal hunting and logging in the Reserve.