An analysis is given of propagation in multimode optical fibres having finite transmission loss. Using experimentally-deduced values for the cladding loss, fibre dispersions are calculated for a range of input beam widths and are compared with experiment. It is shown that the core loss has little effect on dispersion. Cladding loss reduces dispersion for a relatively small increase in attenuation, while dispersion and attenuation become non-linear functions of length.