Paliperidone: 3-{2-[4-(6-fluoro-1,2-benzoxazol-3-yl)piperidin-1-yl]eth-yl}-9-hy-droxy-2-methyl-1,6,7,8,9,9a-hexa-hydro-pyrido[1,2-a]pyrimidin-4-one.

The title compound (also known as 9-hy-droxy-risperidone), C(23)H(27)FN(4)O(3), is a heterocyclic compound with manifold pharmacological properties. The hy-droxy group shows disorder over two positions, with site-occupancy factors of 0.856 (2) and 0.144 (2). The piperidine ring adopts a chair conformation, while the annulated ring bearing the hy-droxy group is present in a half-chair conformation. Classical O-H⋯O hydrogen bonds as well as C-H⋯N contacts connect the mol-ecules into undulating sheets lying perpendicular to the crystallographic b axis. The shortest centroid-centroid distance between two centers of gravity is 3.5867 (8) Šand is apparent between the benzoxazole moiety and the six-membered ring bearing the keto substituent.