Theoretical Λ-doubling parameters ( pv and qv) and centrifugal distortion parameters ( pDv and qDv) are computed for all vibrational levels ( v ≤ 15) of the X2Π ground state of OH. All calculations were carried out using extended basis sets of Slater-type orbitals and rather large configuration-interaction wave functions. The contributions of five perturbing 2Σ states, namely A 2Σ +, (1) 2Σ -, B2Σ +, C2Σ +, and D2Σ - are explicitly included. Although agreement with the available experimental data is excellent (within several percent), the inherent inaccuracies in computing off-diagonal matrix elements involving the L+ and H50 operators preclude the prediction of Λ-doubling transitions with sufficient accuracy (a few Mhz) to reliably aid radioastronomers. The unique perturber or pure precession approximation breaks down as the OH molecule is dissociated, but the infinite second-order sums do appear converged with the inclusion of several 2Σ states.