The greatest challenge in onion breeding programs is achieving gains from plant selection in an efficient manner. Selection indices are already in use for many species but are rare in onion. The aim of this study was to characterize the gain from selection in onion germplasm through nonparametric indices. To bring about this dynamic, four experiments were conducted with different sets of genotypes. Several agronomic characteristics were evaluated. Estimates of gains and selection of genotypes were obtained from the selection index based on rank sum, from the genotype-ideotype distance index, and from the multiplicative index. To test the efficiency of the indices used, the coefficient of coincidence was calculated. The total gains from selection were greater through use of the multiplicative index, with values of 31.84% for the advanced lines and 37.4% for the segregating genotypes. It was possible to select superior onion lines in each experiment. The coefficients of coincidence, all with values greater than 0.5, confirmed that the indices provided a margin of safety in the selection of superior genotypes.