Lowland East Cushitic is often grouped with Highland East Cushitic (the Sidamic languages), Dullay, and Yaaku as East Cushitic, but that group is not well defined and considered dubious.
The most prominent Lowland East Cushitic language is Oromo, with about 35 million speakers in Ethiopia and Kenya. The Konsoid dialect cluster is closely related to Oromo. Other prominent languages include Somali (spoken by ethnic Somalis in Somalia, Ethiopia, Djibouti, and Kenya) with about 15 million speakers, and Afar (in Ethiopia, Eritrea and Djibouti) with about 1.5 million.
Robert Hetzron has suggested that the Rift languages (South Cushitic) are a part of Lowland East Cushitic, and Kießling & Mous (2003) have suggested more specifically that they be linked to a Southern Lowland branch, together with Oromo, Somali, and Yaaku–Dullay.
The vocabulary of the mixed register of Mbugu (Ma'a) may also be East Cushitic (Tosco 2002), though the grammatical basis and the other register are Bantu.
Unclassified within the Lowland languages are Girirra and perhaps the endangered Boon.
Savà and Tosco (2003) believe Ongota is an East Cushitic language with a Nilo-Saharan substratum—that is, that Ongota speakers shifted to East Cushitic from an earlier Nilo-Saharan language, traces of which still remain. However, Fleming (2006) considers it to be an independent branch of Afrasiatic.