The indeterminate growth habit of most cultivars of narrow-leafed lupin (Lupinus angustifolius) results in undue competition between pod growth and branch growth, and sometimes poor partitioning of dry mass to grain. Selection of restricted-branching genotypes has been proposed as a method to overcome this problem. The restricted branching (RB) trait occurs in two forms, mild and severe. This paper reports the pattern of genetic control of mild RB derived from a number of independent sources. The trait, as indicated by the number of leaves on the uppermost branch, was found to be quantitative (quasi-continuous), but highly heritable, and largely controlled by additive genetic effects. There was no consistent correlation of this trait with the number of leaf nodes on the main stem or the time to flowering. It should therefore be possible to obtain different combinations of branching pattern and maturity date through plant breeding, and to assess their adaptation to a range of environments.