Three polymorphs are involved in the construction of the phase diagram describing the enantiotropic and monotropic behavior of the malonamide system, discussed as a function of the temperature and the pressure. The few data available on the orthorhombic metastable form fosters discussion about the domain of stability of this polymorph and about the pressure-induced phase transformation. But previous calculations carried out on this system, along with the method presented here allow proposing the most probable stable phase diagram of malonamide. (C) 2014 Elsevier B.V. All rights reserved.