We retrospectively investigated the prognostic value of the metabolic bulk volume (MBV), defined as the metabolic volume of the largest lesion, in 106 patients with diffuse large B-cell lymphoma who underwent baseline 18FDG PET-CT. Semi-automatically segmented (41% SUVmax) total metabolic tumor volume (TMTV) and MBV underwent receiver operating characteristic analysis, identifying optimal thresholds of 147 cm3 for the TMTV and 41.5 cm3 for the MBV. A low TMTV and a low MBV were significantly associated with longer progression-free survival (PFS) and overall survival (OS). According to Cox multivariate analysis, the TMTV and MBV were independent predictors, respectively, for PFS (HR = 3.501), and OS (HR = 7.242). The TMTV and MBV classification were discordant in 18.9% of patients with a 5-year PFS rate of 100% for patients with low MBV/high TMTV and 74% for high MBV/low TMTV. The baseline MBV can be an efficient tool for the risk stratification of aggressive lymphoma.