We aimed to identify genetic variation in root growth in the cereal crop barley (Hordeum vulgare L.) in response to the early phase of salinity stress. Seminal root elongation was examined at various concentrations of salinity in seedlings of eight barley genotypes consisting of a landrace, wild barley and cultivars. Salinity inhibited seminal root elongation in all genotypes, with considerable variation observed between genotypes. Relative root elongation rates were 60–90% and 30–70% of the control rates at 100 and 150 mM NaCl, respectively. The screen identified the wild barley genotype CPI71284–48 as the most tolerant, maintaining root elongation and biomass in response to salinity. Root elongation was most significantly inhibited in the landrace Sahara. Root and shoot Na+ concentrations increased and K+ concentrations decreased in all genotypes in response to salinity. However, the root and shoot ion concentrations did not correlate with root elongation rates, suggesting that the Na+ and K+ concentrations were not directly influencing root growth, at least during the early phase of salt stress. The identification of genetic diversity in root growth responses to salt stress in barley provides important information for future genetic, physiological and biochemical characterisation of mechanisms of salinity tolerance.