Lowland East Cushitic is often grouped with
Highland East Cushitic (the Sidamic languages),
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
Konsoid dialect cluster is closely related to Oromo. Other prominent languages include
Somali (spoken by ethnic Somalis in
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
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
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.