Soil salinity limits plant productivity and quality. We evaluated the response of 12 aspen (Populus tremula) families to salt stress in two different soils irrigated for 4-weeks with 0, 80 or 160 mM saline solution. Easily measurable characteristics such as shoot height, leaf number, dry mass as well as the distribution of sodium (Na + ) ions were measured in 5-monthold aspen seedlings raised in controlled greenhouse conditions on two different soils. Growth among families varied significantly, and the interaction between family and soil type was significant. From 2-5 months, leaf number correlated with that of the first month and salinity tolerance. Sodium ions varied significantly within plants and among families; seedlings that accumulated higher Na + concentrations in root had more leaves and lower Na + in shoot. These results suggest that leaf number indicates salt tolerance in young seedlings. Seedling performance was also affected by soil type, especially the root/shoot ratio, suggesting an interaction between salt tolerance and growth medium. This study has identified significant intra-specific variation in salt tolerance of aspen in 160 mM saline and highlighted the potential to select and develop a method for efficient pre-screening of trees to be used in the reclamation of salt-affected land.