Ab initio benchmark calculations are reported for the diatomic hydrides of Al, Si, Ga, and Ge and their negative ions using correlation consistent basis sets and several correlated methods. Adiabatic electron affinities for the 0-0 transition were found to be 0.193, 1.256, 0.131, and 1.251 eV for AM, SiH, GaH, and GeH, respectively, at the RCCSD(T)/aug-cc-pVQZ level of theory. Excitation energies (TO) of the a(1)Delta and b(1)Sigma (+) bound excited states were found to be 0.560 and 1.017 eV for SiH- and 0.595 and 1.026 eV for GeH- at the MRCI + Q/aug-cc-pVQZ level. Selected spectroscopic constants are reported for the eight negative ion states,