In the sunflower, Sclerotinia sclerotiorum is the cause of stem rot and broken stems. Seventeen sunflower hybrids were evaluated in Balcarce, Argentina after mid-stem inoculation. The association between rot length and the rate of stem breakage was calculated. Sunflower hybrids showed considerable differences in the size of the rot lesion developed and in the relative number of broken stems, as determined 20 days after the beginning of flowering (daf). No variability was detected for broken stems, both 6 and 60 days after inoculation. Sunflower plants with greater mid stem rot length had a greater relative number of broken stems. The incidence of broken stems could have been enhanced by the mid-stem rot, especially in those genotypes with the lowest proportion of structural tissues in the stems. The degree of genetic determination suggested that environmental effects influence the length of symptoms less than that the proportion of broken stems determined at 20 daf. The results allowed us to propose a breeding program based on the selection of the most adequate genotypes given their level of resistance to these two characters. A phenotypic selection could be performed on individual plants based on the extent of rotting caused by S. sclerotiorum at the mid-stems. Then, the proportion of broken stems could be scored on F2-derived lines in F3 (F2:3 line).