By 128 BCE the Parthians had emerged temporarily as the de facto leading power throughout the Hellenistic Middle East. Their defeat of Demetrius II’s invasion of Mesopotamia in 138 BCE had furthered their heated rivalry with the Seleucids; however, their destruction of Antiochus VII’s invasion of Mesopotamia and Media in 129 BCE finally ended the threat of the Seleucids to their eastern lands. For the first time in their history, the Parthians considered expanding their hegemony over Armenia, Syria, and the regions along the Eastern Mediterranean coast, thus firmly establishing their unrivaled hegemony. Yet any hopes of immediately occupying these regions quickly vanished because of calamities and miscalculations in the early 120s BCE. Although nomadic incursions ravaged the Iranian plateau in the east throughout the 120s BCE, in the west Phraates II’s sudden release of Demetrius to contest the Seleucid throne in Syria before the death of Antiochus became a political debacle that hindered Parthian influence in the region. Despite the arguments of recent scholarship, Phraates’ decision to release Demetrius was shortsighted and haphazard, and Demetrius never served in Syria as a Parthian vassal. This article is a reevaluation of the western policy of the Parthians in the early 120s BCE and the actions of Demetrius during his second reign concerning the Parthians.