In the title compound, C4H5NO3, the morpholine ring adopts a boat conformation that is distorted towards twist-boat, the boat ends being the two Csp3 atoms of the ring. The molecular packing is stabilized by the establishment of strong intermolecular NH...OC hydrogen bonds, which give rise to centrosymmetric dimers, and a network of weak CH2...OC hydrogen bonds, where each dimer interacts with eight neighbouring morpholinedione rings.