Sunflower head rot (SHR) (Sclerotinia sclerotiorum (Lib.) de Bary) is one of the major diseases affecting this crop worldwide. In spite of reports of different levels of susceptibility among sunflower genotypes, there is no evidence of complete resistance in any commercial hybrid. The aim of this work was to evaluate the number of infection courts and the length of the susceptible period in two genotypes with contrasting but stable SHR susceptibility. Repeated experiments during three years in the field included the sunflower hybrids Paraíso-20, moderately resistant, and Rancul, susceptible. Plants were inoculated with ascospores by spray application. Only one or two infection courts were found in each infected sunflower head and this feature did not distinguish cultivar susceptibility. Differences between cultivars were detected considering the length of the susceptible period based on disease incidence higher than zero (LSP) or higher than 10% (LSP10) in two out of three years. LSP was longer in Rancul (28 days) than in Paraíso-20 (17 days). Also LSP10 was longer in Rancul (22 days) than in Paraíso-20 (9 days). The suitability of these two features as components of partial resistance is discussed.