This study tested the hypothesis that B. cinerea shows host specialization on tomato and lettuce, using phenotypic and genotypic tools. Strains were isolated from tomato and lettuce grown together in a same greenhouse. Forty-four lettuce strains and forty-two tomato strains were investigated for their genetic diversity and their aggressiveness. Both gene diversity and allelic richness were significantly higher in lettuce strains than in tomato strains (P=0.01). Cluster analysis revealed a clear structure of the strains under study in two clusters. However, this structure did not separate the strains according to their host of origin. Tomato strains were significantly more aggressive than lettuce strains when inoculated on tomatoes (P=0.001). But no significant differences in aggressiveness were observed when the strains were inoculated on lettuce (P=0.17) or on apple (P=0.87). Our results suggest an absence of clear host specialization of B. cinerea on tomato and lettuce.