Density functional theory with relativistic corrections has been used to calculate the Pt-195 chemical shifts for a series of Pt(II) complexes. Good agreement with experimental values is observed with two different relativistic correction methods. Deconvolution of the parameters leading to the overall shielding of the platinum nucleus shows that both the paramagnetic and the spin-orbit shielding terms contribute substantially. Detailed transition analysis demonstrates that the most important contributions to the paramagnetic shielding for PtX42- anions and cis- and trans-PtX2(NH3)(2) compounds come from the Pt d(xy)-X lone pair pi --> Pt d(x2-y2)-X sigma* and Pt d(xy)-X lone pair pi* --> Pt d(x2-y2)-X sigma* transitions, in accord with qualitative predictions. For cis-and trans-PtX2L2 complexes (L = PMe3, AsMe3, SMe2), the Pt d(xy)-X lone pair pi --> Pt d(x2-y2)-X sigma* transition is most important, but the Pt d(xy)-X lone pair pi* --> Pt d(x2-y2)-X sigma* transition is much less so. This is readily understood through recognition of the importance of the magnetic coupling term to the paramagnetic shielding. The trend that chemical shifts vary as I- < Br- < Cl- arises from the magnetic coupling term and the spin-orbit contribution; it runs counter to the trend predicted by the energy gaps between the orbitals involved in the important transitions.