Priority Primate Areas are identified in Tanzania, mainland Africa's most important country for conservation of primates, on the basis of occupancy by globally rare, Red-Listed and range-restricted primate species and subspecies. We provide a comprehensive list and regional assessment of Tanzania's primate taxa, using IUCN Red List criteria, as well as the first national inventory of primates for 62 sites. The Priority Primate Areas, encompassing 102,513 km2, include nine national parks, one conservation area, seven game reserves, six nature reserves, 34 forest reserves and five areas with no official protection status. Primate species were evaluated and ranked on the basis of irreplaceability and vulnerability, using a combination of established and original criteria, resulting in a primate Taxon Conservation Score. Sites were ranked on the basis of summed primate scores. The majority (71%) of Priority Primate Areas are also Important Bird Areas (IBAs), or part of an IBA. Critical subsets of sites were derived through complementarity analyses. Adequate protection of just nine sites, including six national parks (Kilimanjaro, Kitulo, Mahale, Saadani, Udzungwa and Jozani-Chwaka Bay), one nature reserve (Kilombero) and two forest reserves (Minziro and Mgambo), totalling 8,679 km2, would protect all 27 of Tanzania's primate species. The addition of three forest reserves (Rondo, Kilulu Hill and Ngezi) and two game reserves (Grumeti and Biharamulo), results in a list of 14 Priority Primate Areas covering 10,561 km2 (1.1% of Tanzania's total land area), whose conservation would ensure the protection of all 43 of Tanzania's species and subspecies of primates.