Recently the issue of radiative corrections to leptogenesis has been raised. Considering the "strong washout" regime, in which OPE-techniques permit to streamline the setup, we report the thermal self-energy matrix of heavy right-handed neutrinos at NLO (resummed 2-loop level) in Standard Model couplings. The renormalized expression describes flavour transitions and "inclusive" decays of chemically decoupled right-handed neutrinos. Although CP-violation is not addressed, the result may find use in existing leptogenesis frameworks. * Presented at the International Workshop Frontiers in Perturbative Quantum Field Theory, 10-12 September 2012, Bielefeld, Germany.† The situation is analogous to that for CP-violation in phase transition-based baryogenesis [15,16,17].In efforts towards systematic leptogenesis, the right-handed neutrino self-energy plays an important role [22,23,24]. Examples of recent discussions can be found in sec. 3 of ref. [13] and in sec. 4.1 of ref. [14], in both of which the self-energy was handled at leading order in Standard Model couplings. In the temperature regime of interest, right-handed neutrinos are out of equilibrium, but the Standard Model particles are in equilibrium, at least as far as CP-conserving reactions are concerned. Therefore the self-energy of the right-handed neutrinos, which reflects the dynamics of the other particles, can be computed with established techniques of thermal field theory, and there is no reason to restrict to leading order.In this note a result for the thermal right-handed neutrino self-energy in the non-relativistic regime is presented at NLO (partly even NNLO) in Standard Model couplings. Compared with our earlier work [21], where the production rate of right-handed neutrinos was computed, the real part of the self-energy is added here, and the full Lorentz and flavour structures are included. Technically, we work at order O(h † ν h ν ) in neutrino Yukawa couplings, thus addressing CP-conserving processes, whereas CP-violation originates at the order O(h † ν h ν ) 2 . As an outlook, the same observable could in principle also be computed in the "relativistic" (πT ∼ M ) and ultrarelativistic (πT ≫ M ) regimes; its physics is related to "CP even damping and time evolution", as discussed e.g. in secs. 5.2-3 of ref. [25].