Structural parameters, standard entropies, and vibrational spectra of cyanides and isocyanides of trivalent Al, Ga, and In were obtained for the first time by ab initio and B3LYP density functional methods. The isocyanide form is found to be preferable for Al; for Ga and In, the cyanide form is more stable. The considerable discrepancy between the results obtained by the SCF and B.