Technical Abstract: Lettuce drop is an economically important disease of lettuce (Lactuca sativa L.), and cultivars with resistance to mycelial infection by Sclerotinia sclerotiorum (Lib.) de Barry and S. minor Jagger as well as to S. sclerotiorum ascospores are needed. Assessing resistance in field experiments can be complicated by fast bolting or small stature lettuce lines that may escape, rather than resist the pathogens. Therefore, methods to select resistant lines from morphologically variable populations are needed. We used S. sclerotiorum and S. minor infested field experiments, regression analysis, field experiments with artificially high plant densities, and S. sclerotiorum ascospore inoculations to identify lettuce lines with resistance to both pathogens. Three replicated S. sclerotiorum field experiments were conducted in Yuma, AZ and three S. minor field experiments were conducted in Salinas, CA using diverse populations of iceberg, romaine, leaf, butterhead, latin, oilseed lettuce and wild relatives of lettuce; genetic variation for the incidence of lettuce drop from mycelial infections was identified. In two S. minor field experiments, bolting was rated on a 1 (rosette plants) through 6 (seed set) scale, and a quadratic regression model was developed that related faster bolting with reduced lettuce drop. Regression residuals were calculated, and ‘Eruption’, ‘Little Gem’, PI167391, PI176592, PI178921, PI226641, PI229761, and PI273589 had negative residuals, indicating higher resistance than predicted by their stage of bolting. Eruption, a small statured Latin cultivar, had significantly lower disease than susceptible cultivars in experiments with high plant densities, indicating that its small size did not facilitate disease escape. Ascospore inoculations confirmed resistance in ‘Eruption’ and L. virosa SAL012, while the oilseed lettuce PI251246 may have partial resistance to infection.