The geometric structure of malonamide, NH2C(O)-CH2-C(O)NH2, has been investigated by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximations with 6-311++G(3df,pd) basis sets). Both GED and quantum chemistry result in the existence of a single diketo conformer in the gas phase. According to GED refinement this conformer possesses (sc,ac) conformation with one CO bond in synclinal orientation (dihedral angle tau(OC-C-C) = 49.0(3.0)degrees) and the other CO bond in anticlinal orientation (dihedral angle tau(OC-C-C) = 139.5(3.3)degrees). The experimental geometric parameters are reproduced very closely by the B3LYP method.