Phytophthora blight, primarily caused by Phytophthora nicotianae, poses a significant threat to Helleborus production under warm and humid conditions. However, the tolerance levels of different Helleborus cultivars to this disease have not yet been compared. Thus, this study aimed to assess disease tolerance in the 17 major Helleborus cultivars available in Japan, all propagated via tissue culture to ensure genetic uniformity. The plants were inoculated with P. nicotianae, and the disease progression was monitored over 20 days. Our results revealed substantial variation in disease severity among the cultivars. The ‘Petit doll’ cultivars, particularly ‘Petit doll Shiori,’ exhibited strong and consistent tolerance, whereas the others, such as ‘White sugar chiffon’ and ‘Mayuhiki,’ showed high susceptibility. Some cultivars displayed delayed symptom development followed by rapid progression. In several cases, discrepancies were observed between root and foliar symptoms, indicating that above- and below-ground responses do not always correlate. This highlights the diversity of disease responses and the need for integrated evaluation methods when screening for disease tolerance. The tolerant cultivars identified in this study are valuable resources for breeding programs to improve resistance and ensure the sustainability of Helleborus production.