The Horn of Africa ( alternatively Northeast Africa , and sometimes Somali Peninsula ) is a peninsula in East Africa that juts for hundreds of kilometres into the Arabian Sea , and lies along the southern side of the Gulf of Aden . The Horn of Africa ( alternatively Northeast Africa , and sometimes Somali Peninsula ; shortened to HOA ) is a peninsula in East Africa that juts hundreds of kilometers into the Arabian Sea and lies along the southern side of the Gulf of Aden .