We extend the full triples equation-of-motion (EOM) coupled cluster (CC) method to electron attached states. Proper factorization of the three- and four-body parts of the effective Hamiltonian makes it possible to achieve for the EA-EOM part a scaling no higher than n(occ)(2)n(vir)(5). The method is calibrated by the evaluation of the valence vertical electron affinities for the C-2 and O-3 molecules for several basis sets up to 160 basis functions. For C-2, EA-EOM-CCSDT gives 3.24 eV at the extrapolated basis limit, while the experimental adiabatic EA is equal to 3.27+/-0.008 eV. For O-3 the agreement is similar to1.9 eV compared to an adiabatic value of 2.1 eV. (C) 2003 American Institute of Physics.