Abstract: If disc galaxies are optically thick in their central regions then their luminosity profiles in, say, the B band will not reflect the true underlying distributions of stars. In galaxies with known gas distributions we can attempt to correct for the associated dust absorption. By following this procedure for some well-studied objects we can gain an insight into how dramatic the optical depth effects on luminosity profiles can be. In particular we find that (1) in all cases looked at (which include galaxies with a wide range of ISM densities) the extrapolated central surface brightnesses of the discs are brightened by about 0.8 mag (i.e. a factor 2) and (2) galaxies with Type II luminosity profiles (i.e. those with a dip or shoulder near the centre, relative to the inward extrapolation of the outer disc component) have ‘normal’ bulge plus disc profiles after the absorption corrections have been applied. As a check on this ‘missing light’, we also present a comparison with profiles obtained from IRAS data; in all cases there is an excellent correspondence between the light lost from the B band, as predicted by our optically thick disc models, and that (re)emitted in the far infrared.