The Ibadan Malimbe Malimbus ibadanensis is a globally Endangered but poorly known forest species endemic to a small region of south-western Nigeria, where almost all forest has been severely fragmented. We carried out the first comprehensive survey of Ibadan Malimbe, and tested whether forest fragmentation is important in determining the distribution of this and related species in south-west Nigerian forest patches. Ibadan Malimbes were found at 19 of 52 sites surveyed but these were all clustered in a relatively small part of what appears to have been the former range. Unlike other malimbes, Ibadan Malimbes were less abundant in, or absent from, relatively isolated forest patches. Red-headed Malimbe M. rubricollis, Red-vented Malimbe M. scutatus and Crested Malimbe M. malimbicus were significantly more abundant in forest patches that retained vegetation characteristic of primary forest (i.e. tall trees and high tree densities). The average density of Ibadan Malimbes was 0.22 birds/ha (95% confidence limits (CL): 0.14–0.34) across all sites, but varied with degree of isolation, with densities of 0.06 birds/ha (0.03–0.14) in the 50% of fragments that were most isolated, compared with 0.33 (0.19–0.56) in the 50% of fragments that were least isolated. This gives a population estimate of 2,469 individuals (1,401–4,365) for the remaining potentially occupied forest area of 112 km2. Given that our survey covered most forest patches within the majority of the historical range of Ibadan Malimbe this can probably be considered a reasonable maximum world population estimate. Ibadan Malimbes appear to be restricted to a small number of relatively small forest patches most of which are highly vulnerable to further destruction, degradation and fragmentation. Conservation effort should urgently focus on the protection of currently occupied sites and increasing the number and extent of forest patches within and around the existing range.