We present the first assessments of the population, distribution and conservation status of the recently described kipunji Rungwecebus kipunji in forests in the Southern Highlands and Udzungwa Mountains of southern Tanzania. Surveys totalling 2,864 hours and covering 3,456 km of transects were undertaken to determine distribution and group numbers, following which 772 hours of simultaneous multi-group observations in Rungwe-Kitulo and Ndundulu forests, in the Southern Highlands and Udzungwa Mountains respectively, enabled 209 total counts to be carried out. We estimate there are c. 1,042 individuals in Rungwe-Kitulo, with 25–39 individuals per group (mean 30.65 ± SE 0.62, n = 34), and 75 individuals, with 15–25 per group (mean 18.75 ± SE 2.39, n = 4) in Ndundulu. We estimate a total kipunji population of 1,117 in 38 groups, with 15–39 per group (mean 29.39 ± SE 0.85, n = 38). The Ndundulu population may no longer be viable and the Rungwe-Kitulo population is highly fragmented, with isolated sub-populations in degraded habitat. We recorded areas of occupancy of 1,079 and 199 ha in Rungwe-Kitulo and Ndundulu, respectively, giving a total of 1,278 ha. We estimate the species’ extent of occurrence to be 1,769 ha, with 1,241 and 528 ha in Rungwe-Kitulo and Ndundulu, respectively. We believe the kipunji faces an extremely high risk of extinction in the wild and recommend the species and genus be categorized as Critically Endangered on the IUCN Red List.