The mass of the ηc meson is calculated by means of QCD sum rules. If the spectrum of the 0- states of charmonium contains a single prominent resonance, like the J ψ in the case of vector states, then the ηc mass is 3.0 GeV, not 2.83. There is a possibility however that there are two mixed 0- states with close masses. Then the X(2.83) could be one of them. The other one however has a much larger coupling to the pseudoscalar current of c quarks and is a "true" ηc. The ηc mass in the case of two mixed states is 3.0-3.2 GeV.