UBV photometry for stars in the globular cluster NGC 6981 = M72 is presented. Another paper describes results of B V photometry for 21 RR Lyrae variables in the cluster. The colour-magnitude diagram shows a horizontal branch populated on both sides of the variable star region. The two-colour (U-B/B-V) diagram for field stars is used to derive a reddening of E(B-V) = i mag, and the two-colour diagram for cluster giants used to derive an ultra-violet excess of (U-B) = mag at (B-V)0 = . The latter value shows that the cluster is relatively metal rich, in agreement with the integrated spectral type of G3 but contrary to the Morgan II classification. A discussion of some problems associated with the interpretation of HR diagrams and other parameters of globular clusters in terms of current evolutionary theory is given.