Orestheus^{[pronunciation?]} (Ancient Greek: Ὀρεσθεύς derived from oresteros "mountainous" from όρος oros "mountain, hill"), in Greek mythology, was a name attributed to two individuals.

• Orestheus, a king of the Ozolian Locrians in Aetolia. He was the son of Deucalion and Pyrrha, the legendary progenitors of the Greek race. Orestheus was the brother of Pronous and Marathonius.^[1] His dog was said to have given birth to a piece of wood which he concealed in the earth. In the spring, a vine grew forth from it, from the sprouts of which (Greek ὅζοι ozoi "branches") Orestheus derived the name of his people.^[2]
• Orestheus, an Arcadian prince as one of the 50 sons of the impious King Lycaon either by the naiad Cyllene,^[3] Nonacris^[4] or by unknown woman. He was the reputed founder of Arcadian Oresthasion, which is said afterwards to have been called Oresteion, from Orestes.^[5]