Barley landraces from the western Mediterranean area have not been thoroughly exploited by modern breeding. This study aims at assessing the agronomic value of a core collection of lines derived from landraces of Spanish origin and to compare them with sets of successful old and modern cultivars. The agronomic performance of a set of 175 barley genotypes, comprising 159 landrace-derived lines and 26 cultivars, was evaluated in a series of 10 field trials, carried out over 3 years and several locations. The most relevant trait of the landraces was higher grain yield at low production sites than cultivars, which may be related with better ability to fill the grain under stressful conditions. On the other hand, lateness, excessive plant height and lodging were negative traits frequently found in the landraces. Large genotype-by-environment interaction (GEI) for grain yield was detected, related partly with differences between germplasm groups, probably indicating local adaptation. GEI was also associated with the interaction of heading time and powdery mildew resistance with temperature.