Worldwide, salinity is a major environmental stress affecting agricultural production. Sodium (Na+) exclusion has long been recognised as a mechanism of salinity tolerance (ST) in cereals and several molecular markers have been suggested for breeding. However, there have been no empirical studies to show that selection for Na+ exclusion markers could improve grain yield in bread wheat under dryland salinity. In six field trials, a bread wheat mapping population was grown to validate Na+ exclusion quantitative trait loci (QTL) identified earlier in hydroponics, to determine the impact of Na+ exclusion on grain yield, and to identify QTL for yield-related traits. The traits included grain yield, grain number per m2, 1,000-grain weight, maturity, plant height, and leaf Na+ and K+ concentrations. The presence of numerous QTL with minor effects for most traits indicated the genetic complexity of these traits, and thus limited prospects for pyramiding at present. Considerable QTL-by-environment interactions were observed, with the stable QTL generally being co-located with maturity or early vigour/height genes, which demonstrates the importance of measuring major agronomic traits in order to discover genuine QTL for ST. Several QTL for seedling biomass and Na+ exclusion identified earlier in hydroponics were also detected in field trials but with marginal impact on grain yield. These results suggest that selection for Na+ exclusion and the use of hydroponics-based seedling assays may not necessarily result in improved ST. However, as this is the first report of its kind, there is an urgent need for testing other mapping populations in realistic environments to discover novel ST-QTL for breeding programs. In the meantime, grain yield QTL independent of maturity and height may offer potential to improve ST.