The Dunham parameters of the ground state of the CO molecule are determined by a least squares fit of recent high-quality microwave and heterodyne frequency measurements. It is shown that these new parameters are more accurate than others obtained recently. Revised equilibrium molecular constants have been deduced from these new Dunham parameters and the mass-scaling coefficients determined by Guelachviliet al.The most important constants are ωe= 65 047 645(7) MHz, ωexe= 398 365·1(14) MHz, ωeye= 312·11(14) MHz,Be= 57 907·98(6) MHz, αe= 524·791(13) MHz,De= 0·183 520 8(57) MHz andRe= 1·128 243(1) Å. The new ground state parameters allow precise determination of the transition frequencies, which can now be used as secondary standards in the microwave and infrared ranges.