A theoretical study has been carried out on the electronic and molecular structure of the hydroformylation catalyst HCo(CO)3 as well as the parent molecule HCo(CO)4. The study was based on a nonlocal Density Functional (DF) method. The parent molecule has a trigonal bipyramidal structure with hydrogen in the axial position. The catalyst HCo(CO)3 adopts a singlet ground state with a geometry of Cs symmetry where one equatorial CO groups has been removed from HCo(CO)4. The other singlet structure of C3v symmetry with an axial CO group removed from HCo(CO)4 is 35 kJ mol-1 higher in energy. Optimizations have further been carried out on five triplet states of HCo(CO)3 , they are found to be ~ 100 kJ mol-1 higher in energy than the Cs singlet structure. Calculations have also been carried out on the IR spectra of HCo(CO)4 and HCo(CO)3, in order to interpret the low temperature vibrational spectra obtained in a krypton matrix after photolysis of HCo(CO)4. The following bond energies have been obtained for HCo(CO)4 : De(Co-COax) = 207 kJ mol-1 , De(Co-COeq) = 169 kJ mol-1 and De(Co-H) = 288 kJ mol-1