Purpose To test and compare the association between radiologic measurements of lesion diameter, volume, and enhancement on baseline magnetic resonance (MR) images with overall survival and tumor response in patients with unresectable hepatocellular carcinoma (HCC) treated with transarterial chemoembolization (TACE). Materials and Methods This HIPAA-compliant retrospective, single-institution analysis was approved by the institutional review board, with waiver of informed consent. It included 79 patients with unresectable HCC who were treated with TACE. Baseline arterial phase contrast material-enhanced (CE) MR imaging was used to measure the overall and enhancing tumor diameters. A segmentation-based three-dimensional quantification of the overall and enhancing tumor volumes was performed in each patient. Numeric cutoff values (5 cm for diameters and 65 cm(3) for volumes) were used to stratify the patient cohort in two groups. Tumor response rates according to Response Evaluation Criteria in Solid Tumors (RECIST), modified RECIST (mRECIST), and European Association for the Study of the Liver (EASL) guidelines were recorded for all groups. Survival was evaluated by using Kaplan-Meier analysis and was compared by using Cox proportional hazard ratios (HRs) after univariate and multivariate analysis. Results Stratification according to overall and enhancing tumor diameters did not result in a significant separation of survival curves (HR, 1.4; 95% confidence interval [CI]: 0.7, 2.5; P = .234; and HR, 1.6; 95% CI: 0.9, 2.8; P = .08, respectively). The stratification according to overall and enhancing tumor volume achieved significance (HR, 1.8; 95% CI: 0.9, 3.4; P = .022; and HR, 1.8; 95% CI: 1.1, 3.1; P = .017, respectively). As for tumor response, higher response rates were observed in smaller lesions compared with larger lesions, when the 5-cm threshold (27% vs 15% for mRECIST and 45% vs 24% for EASL) was used. Conclusion As opposed to anatomic tumor diameter as the most commonly used staging marker, volumetric assessment of lesion size and enhancement on baseline CE MR images is strongly associated with survival of patients with HCC who were treated with TACE.