Oxymorphone (oxymorphone hydrochloride) (14-hydroxy-dihydromorphinone), a semisynthetic mu-opioid agonist, was first approved by the US Food and Drug Administration in 1959. Oxymorphone is considered a more potent opioid than its parent compound, morphine. Recently, an immediate-release and long-acting oral formulation of this drug was developed that makes oxymorphone a new option in treating moderate to severe pain. This article reviews the pharmacodynamics, pharmacology, and clinical efficacy for this new option in treating moderate to severe pain.