The objective of this work was to estimate yield losses in sunflowers caused by sclerotinia head rot. Subplots with different levels of disease intensity (percentage of plants with head rot) were generated by inoculations utilizing different environmental conditions and genetic materials (five commercial hybrids). Seed yield, seed oil content, weight per 1,000 seeds, dockage percentage, and oil acidity were recorded in the inoculated subplots and in the healthy ones, which were used as controls. Highly posiûve correla tions between percentage of diseased plants and reduction in seed yield (1=Q.76***), increase in dockage (r=0.67***), and oil acidity levels (r=O.58***) were found. Yield reduction estimates varied among hybrids; this indicates that they are genetically different for their tolerance to head rot. The obtained results permit to state that head rot causes direct (seed yield reduction) and indirect (increase in dockage and oil acidity levels) damages to the sunflower crop. An inverse relation would exist between the magnitude of both types of damage. That is, when capitula are completely disintegrated, there would be no indirect damages, whereas if the development of the disease is slow (high genotypic tolerance, unfitted environmental conditions for the pathogen or both), indirect damages would be greater since more heads can be harvested. It is concluded that sunflower breeding for head rot control must be oriented to select those genot5æes with better resistance levels (in terms of lower percentage of diseased plants) rather than to select genot5æes with better tolerance levels (in terms of yield losses).