Tthe structure of the title compound, C(15)H(24)O(5), has been redetermined at 103 (2) K, with much improved precision. The title compound was first reported by Luo, Yeh, Brossi, Flippen-Anderson & Gillardi [Helv. Chim. Acta (1984). 67, 1515-1522]. It is a derivative of the anti-malaria compound artemisinin and consists primarily of three substituted ring systems fused together. A cyclo-hexane ring (with a distorted chair conformation), is fused to a tetra-hydro-pyran group (also with a distorted chair conformation), and is adjacent to an oxacyclo-heptane unit containing an endoperoxide bridge. This gives the mol-ecule a unique three-dimensional arrangement. The crystal packing is stabilized by inter-molecular C-H⋯O and O-H⋯O inter-actions between an H atom from the cyclo-hexane ring and an O atom from the endoperoxide bridge, as well as between the hydroxyl H atom and an O atom from a tetra-hydro-pyran ring.