Steatohepatitis enhances the severity of liver injury caused by acute inflammation. The purpose of this study was to test the hypothesis that fatty liver due to chronic choline‐deficient diet exacerbates concanavalin A (ConA)‐induced liver hepatitis, which is predominantly facilitated by T cells. Male C57BL/6 mice were fed either control choline‐sufficient diet (CSD) or choline‐deficient diet (CDD) for 6 weeks before ConA administration. Mice were sacrificed 3, 9, and 24 hours after ConA injection. Liver injury measured by aspartate aminotransferase (AST), alanine aminotransferase (ALT), pathology, and terminal deoxynucleotidyl transferase‐mediated nick‐end labeling (TUNEL) staining was minimal in mice fed either diet before ConA exposure. However, ConA‐induced liver injury was significantly greater in CDD‐fed mice compared with control‐fed mice. Liver cytokines were assessed by quantitative real‐time polymerase chain reaction (PCR). The expression of T helper (Th) 1 cytokines tumor necrosis factor alpha (TNF‐α), interleukin 12 (IL‐12), and interferon gamma (IFN‐γ) were dramatically elevated after ConA in CDD‐fed mice compared with control‐fed mice. CDD also enhanced ConA‐induced STAT4 activation, but not STAT6. Notably, regulators of T‐cell differentiation were strongly shifted toward a predominant Th1 profile. T‐bet, regulator of the Th1 response, was up‐regulated in CDD‐fed mice, whereas Th2 regulator GATA‐3 was significantly suppressed in CDD‐fed mice after ConA. Moreover, the expression of suppressor of cytokine signaling (SOCS)‐1, SOCS‐3, and repressor of GATA‐3 (ROG) favored a predominant Th1 cytokine response in CDD‐fed mice. In conclusion, these data support the hypothesis that hepatosteatosis caused by CDD is associated with more severe ConA‐induced hepatitis due to a predominant shift toward Th1 response. (HEPATOLOGY 2006;44:216–227.)