An electronic absorption spectrum of FO has yet to be observed experimentally but as a guide for future spectroscopic studies of this radical, CASSCF/MRCI ab initio calculations have been performed to locate and identify the lowest energy valence and Rydberg states. No bound valence excited potentials were found save the a(4)Sigma(-) state. The calculations provide estimates of the transition energies T-e to the lowest Rydberg states and the wavelengths required for spectroscopic detection. Results for both the doublet and quartet states are presented, revealing the 3s sigma, 3p pi, 3p sigma, 3d delta, 4d sigma, 3d pi, and 4d delta Rydberg orbitals. It is likely that the repulsive valence states 1(2)Sigma(-) and 1(2)Delta predissociate the lowest Rydberg states of the same symmetry. Consequently, the 2 Pi Rydberg states, three of which are found here, are the most promising candidates for optical detection.