DSC measurements have revealed that d- and l-carvone form mixed crystals at all compositions corresponding to a phase diagram with a minimum. The thermodynamic data of the equimolar mixture, however, are not reproducible, Therefore, in this study the dependency of the thermodynamic data on thermal history was investigated by means of adiabatic calorimetry. The measurements revealed the polymorphic behaviour of the formed crystalline material. Metastable dl-carvone melts at (231 +/- 0.5) K and the stable form at (241.15 +/- 0.05) K. The heats of melting are (8.98 +/- 0.05) and (12.697 +/- 0.005) kJ mol(-1) for the metastable and stable forms respectively. The heat capacities of the stable form were determined from 4 K up to room temperature; the stable form does not show any phase transition before melting.