Observations with the Molonglo and Parkes radio telescopes have recently produced improved radio frequency data for the southern galactic supernova remnants (SNRs). We have now used these observations to investigate the general evolutionary properties of SNRs—the first such large-scale analysis based on a near-homogeneous data set. Empirical relationships are derived which describe in general terms the expansion of SNRs, at least during the adiabatic phase of their evolution. An improved SNR distance scale is established, based largely on Parkes H I absorption measurements, and the resulting relationship between surface brightness and linear diameter for galactic SNRs is found to be compatible with that determined for the Magellanic Cloud SNRs, contrary to earlier conclusions. Completeness in our catalogue down to a uniform level of surface brightness permits an improved estimate of the number of SNRs in the Galaxy and suggests that this number has previously been overestimated. We consequently infer a larger characteristic interval between supernova events (of a kind giving rise to typical radio remnants) of ~ 150 yr. Furthermore, on the assumption that most of the brighter SNRs are in the Sedov adiabatic expansion phase, the typical value of E0/n (ratio of energy released in a supernova outburst to the number density of H atoms in the surrounding interstellar medium) implied by our data is 5 × 1051 erg cm3, which is considerably higher than was commonly assumed in earlier work.