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The lower states of the PdH molecule have been studied with different relativistic methods. At the spin-free level, relativistic effects are shown to be crucial for a proper description of the molecule. PdH is shown to be a single-configuration molecule, but the configuration interaction (CI) results are highly sensitive to the choice of orbital basis. Spin–orbit interaction has been included through spin–orbit CI theory based on the second order Douglas–Kroll operator and through fully relativistic CI calculations based on the Dirac–Coulomb Hamiltonian. The results are in good agreement, but requires a proper choice of orbital basis in the spin–orbit CI calculation to ensure a balanced description of all ΛΣ states coupled by spin–orbit interaction.