We report a force field for HCO in the (B) over tilde (2)A’ electronic state, based on ab initio electronic energies obtained using state-averaged multiconfiguration-self-consistent field/configuration interaction wave functions. The force field is used in rigorous calculations of 27 excited vibrational states of HCO and DCO, which are compared with experiment. A detailed analysis of the fundamentals of HCO and DCO suggests a reassignment of the experimental fundamentals of DCO is necessary.