Background/Aims: King's College Hospital (KCH) criteria and the model for end-stage liver disease (MELD) score are useful and widely-employed prognostic markers for acute liver failure (ALF). We previously reported that liver atrophy is an important prognostic factor for ALF. The aim of the present study was to assess the value of liver volumetry and to generate a new prognostic formula. Methods: Computed tomography-derived liver volume (CTLV) and standardized liver volume (SLV) of 30 adult ALF patients were calculated at the time of diagnosis. Patients were assigned to one of two groups: group A consisted of 13 patients who recovered without surgical intervention, and group B consisted of 17 patients who died due to liver failure or who underwent living donor liver transplantation (LDLT). Results: The median CTLV/SLV ratios of groups A and B were 1.019 and 0.757, respectively (P ฯญ 0.0009). The difference was most significant (P ฯญ 0.0002) at the probability cutoff point of 0.80 for CTLV/SLV ratio; the sensitivity and specificity were 76.5% and 92.3%, respectively. Serum total bilirubin (TB) levels and CTLV/SLV ratio were selected as independent prognostic factors by multivariate analysis. A prognostic formula including volumetric analysis was established: Z ฯญ -2.3813 -[0.15234 ฯซ TB (mg/dl)] ฯฉ [4.5734 ฯซ CTLV/SLV] (AUC ฯญ 0.87783, P ฯญ 0.0002). Conclusions: The CTLV/SLV ratio is a very useful marker for predicting the prognosis of adult ALF. Our prognostic formula including only the CTLV/ SLV ratio and TB is simple and useful and awaits validation in a future larger-scale prospective study.