The micromaser dynamics is studied without assuming the validity of the rotating-wave approximation (RWA). Through numerically evaluating micromaser spectra for first and second order correlations we compare our results with those based on the RWA for both the resonant and the nonresonant case. We find that in the resonant case values of g/ω0-where g is the atom-field coupling constant and ω0 the transition frequency - of the order of 10-3 to 10-4 would be necessary to achieve shifts of the spectra that would be larger than their corresponding linewidths. These shifts arise from typically quantum-mechanical self-energy effects. In the nonresonant case, for detunings of the order of 1 MHz and within a parameter range of current experimental interest (g/ω0 ≈ 10-6) we predict a relative shift, stemming from the Bloch-Siegert effect, for the case of spectra corresponding to two-photon correlations. Furthermore, we find that the RWA and non-RWA cases are clearly resolved from each other when we plot the time evolution of second-order field correlations. These can be put in correspondence with atomic correlations that are measurable through selective field ionization. © 1997 Elsevier Science B.V.