Summary • Ingestion of caesium (Cs) radioisotopes poses a health risk to humans. Crop varieties that accumulate less Cs in their edible tissues may provide a useful countermeasure. This study was performed to determine whether quantitative genetics on a model plant (Arabidopsis thaliana) might inform such ‘safe’-crop strategies. • Arabidopsis accessions and recombinant inbred lines (RILs), from Landsberg erecta (Ler) × Cape Verdi Island (Cvi), Ler × Columbia (Col), and Niederzenz (Nd) × Col mapping populations, were grown on agar supplemented with subtoxic levels of Cs. • Shoot Cs concentration varied up to three-fold, and shoot f. wt varied up to 25-fold within populations. The heritability of growth and Cs accumulation traits ranged from 0.06 to 0.28. Four quantitative trait loci (QTL) accounted for > 80% of the genetic contribution to the total phenotypic variation in shoot Cs concentration in the Ler × Col population. • QTL identified in this study, in particular, QTL co-localizing to the top and bottom regions of Chromosomes I and V in two different mapping populations, are amenable to positional cloning and, through collinearity, may inform selection or breeding strategies for the development of ‘safe’ crops.