A remarkable number of new vertebrate species have been discovered in Tanzania in the last 30 years. These discoveries have mainly been centred in the montane highlands, particularly the Eastern Arc Mountains. More recently, research in the often difficult to access interior of Tanzania has begun to reveal a unique avian community with associated endemic taxa. One such endemic taxon is the collaris race of the White-headed Black Chat Myrmecocichla arnotti. First described by Reichenow in 1882, collaris was found to be morphologically distinct from the nominate form, in that females possess a complete white collar. However, due to a lack of knowledge about the development of adult plumage, the distributional range, and the lack of diagnostic features among males of the different White-headed Black Chat races, collaris specimens were generally considered aberrant, and the name largely disappeared from the literature by 1910. Here, we report the results of morphological and genetic analyses, and detailed observations of this chat in what we now know to be the centre of its distributional range in Ruaha National Park, Tanzania. Our results suggest that all birds from west of the Eastern Arc and southern Tanzanian highlands are of the white-collared form, which we suggest should be accorded species rank and named Myrmecocichla collaris, the Ruaha Chat.