Mutual correlation of the electronic and nuclear motions in an atom is discussed through the average momenta squared of electrons [\Sigma(i)p(i)\(2)] and nucleus [q(0)(2)] and through the correlation coefficient C-en between electron p(i) and nucleus q(0) momenta. The coefficient C-en is shown to be completely determined by the corresponding coefficient C-ee between electron momenta p(i) and p(j). Relations of the correlation coefficients C-en and C-ee with the nuclear mass correction energies are also mentioned. Numerical results of C-en are reported for the 103 atoms from hydrogen to lawrencium. (C) 2003 American Institute of Physics.