The vertical excitation energies are investigated for singlet and triplet states of methylsilane. To analyze the importance of Rydberg functions and of both valence and Rydbergd functions, a sequence of ten different basis sets are considered in conjuction with a single excitation configuration interaction. It is found that all of the singlet states below the first ionization potential may be characterized as Rydberg states, while there is considerable valence character in some of the low‐lying triplets. If the valence s and p functions are represented reasonably well (e.g., with a split valence basis set), the role of valence d orbitals is found to be minor.