We present a theoretical investigation of the band lineups between crystalline and amorphous silicon, based on the first-principles pseudopotential method and the model-solid theory. We find that the offsets are very sensitive to the hydrogen content of the material; the valence-band offset for a junction with unhydrogenated a-Si is -0.25 eV, while for hydrogenated a-Si with a hydrogen content of 11% the offset becomes 0.20 eV. Consequences for the interpretation of experimental data are discussed.