The spin-rovibronic levels of the HCP+ radical cation and its deuteriated isotopomer in the ground X (2)Pi state have been studied using high-level ab initio methods followed by variational calculations on the computed potential energy surfaces. All experimental levels are reproduced within 8 cm(-1) and predictions of the rovibronic levels (Kless than or equal to3) for energies up to 4500 cm(-1) for HCP+ and 4000 cm-1 for DCP+ are provided. Anharmonic resonances are analyzed in detail and found to be more complex than previously thought.