We calculate in closed analytical form the one-loop radiative corrections to electron–electron scattering e−e− → e−e−. Explicit expressions (in terms of dimensionless Mandelstam variables) are given for the pertinent interference terms between the tree diagrams and the one-loop diagrams. Infrared finiteness of these virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cutoff λ. We evaluate the remaining finite part of the soft photon correction factor in the center-of-mass frame. These results can also be utilized for Bhabha scattering e−e+ → e−e+ and for elastic muon scattering μ−μ∓ → μ−μ∓. Furthermore, we calculate in the same way the one-loop radiative corrections to the scattering of unequal leptons e−μ− → e−μ− and apply them likewise to the muon pair production process e−e+ → μ+μ−. In contrast to most other calculations of these radiative corrections we keep the full dependence on the lepton masses. Effects from hard photon radiation which are also important for a direct comparison with (a specific) experiment are not treated explicitly.