I have calculated the correlation energy and effective mass of electrons in a two-dimensional electron gas. The results on the effective mass show good agreement with experiments on Si. However, when the finite thickness of the inversion layer is taken into account the effective mass is reduced. The difference between our results and those recently published by Ting et al. is due to their use of an approximation to the Dyson equation. Dispersion in the insulator and a finite insulator thickness have been considered. © 1975 The American Physical Society.