Aims: This study aimed to quantify the changes in root and aerial biomass of durum wheat brought about by the introduction of the Rht-B1b dwarfing allele and their effects on yield formation. Methods A historical series of 24 Mediterranean cultivars with allelic variants a (tall) and b (semi-dwarf) at Rht-B1 locus was tested in tubes in three greenhouse experiments and six field experiments. Results: The dwarfing allele reduced the aerial biomass of each plant at anthesis by 7.6 % and the root by 28.1 % (25.4 %, 26.7 % and 36.0 % in the upper, middle and lower root sections, respectively). Aerial and root biomass were reduced by 27.0 g y−1 and 7 g y−1 respectively, but the relative rate of change was much greater for roots (−0.73 % y−1) than for aerial organs (−0.17 % y−1). Aerial biomass at anthesis was negatively associated with spike number, harvest index and yield in tall cultivars, but no significant relationship was found for semi-dwarf ones. Conclusions: The root/aerial biomass ratio was 29 % lower in semi-dwarf than in tall cultivars. In tall cultivars large aerial biomass at anthesis was detrimental to yield formation, while in semi-dwarf cultivars high aerial biomass at anthesis had no effect on yield formation.