A qualitative and comparative study of electromagnetic showers simulated the Monte Carlo codes Geant4, EGS5 and AIRES, is presented. Particularly, we simulate the passage through air of electrons or photons of different energies and in the order of the MeVs. As the particle propagates, it gives rise to an electromagnetic shower. We analyse the longitudinal development of the shower, as well as its lateral dispersion and energy distribution. We find that there is a qood qualitative agreement between the three Monte Carlo codes used.