Excitation energies and lifetimes for the 213 lowest states of the n <= 5 configurations in B-like S XII are calculated using highly correlated wave functions, optimized with the fully relativistic multiconfiguration Dirac-Hartree-Fock method. Multipole transition rates and associated radiative data (line strengths and oscillator strengths) for transitions connecting these levels are also reported. The theoretical excitation energies are systematically compared with the NIST Atomic Spectra Database in which misidentifications are pointed out. After eliminating the latter, a mean energy difference with the standard deviation between computed and observed energies of 12 +/- 341 cm(-1) is obtained for the n >= 3 high-lying states. This level of accuracy confirms that elaborate ab initio calculations can assist in the identification of new emission lines in the solar and other astrophysical spectra. The present work provides atomic data of high accuracy for an ion of astrophysical interest, B-like S XII, for which experimental data are scarce.