The isotropic hyperfine splitting constants at the magnetic nuclei C-13 and Si-29 in the permethylcyclotetrasilane radical anion are well reproduced at the UMP2/VTZPD//UHF/VTZPD level of theory. The radical has a pi-type (2)A(2u) electronic configuration. This in contrast to the sigma-type configuration determined by ENDOR spectroscopy on the basis of the small Si-29 hyperfine anisotropy found in peralkylcyclopolysilane radical anions, The components of the hyperfine dipolar tensor A'(Si-29) are computed to be small since the unpaired electron is mainly delocalized into the Si-3p(pi) outer-valence atomic orbitals. The Si-29 hyperfine anisotropy is computed to be 99.5 MHz(2) at the UHF/VTZPD level, in agreement with the ENDOR prediction for peralkylcyclopolysilane anions (30-100 MHz(2)).