AIM To determine whether S-1 induces hepatic steatosis in patients being treated for pancreatic cancer.METHODS This retrospective study evaluated 22 patients who received oral S-1 as a first-line treatment for pancreatic cancer between January 2008 and July 2015 at the Ishikawa Prefectural Central Hospital. Patients underwent abdominal computed tomography(CT) scans before chemotherapy and within 3 mo from the start of treatment. CT numbers of the liver and spleen were measured before and after S-1 administration. Steatosis was diagnosed when the ratio of the CT number of the liver to that of the spleen(liver/spleen ratio) was < 0.9.RESULTS Median patient age was 68 years(range, 48-85 years), and median body mass index was 21 kg/m~2(range, 18-27 kg/m~2). Of the 22 patients, six(27%) regularly consumed alcohol, and five(23%) had liver metastases. The mean ratio of CT number of the liver to the spleen was significantly higher before administration of S-1(1.27 vs 1.09, P = 0.012) compared with after. Of the 22 patients, five(23%) had hepatic steatosis and 17(77%) did not. The pretreatment demographic and clinical characteristics of these two groups showed no significant differences. The relationship between liver/spleen ratio and alanine transaminase activity in these patients. A statistically significant inverse correlation was observed(r =-0.417, P < 0.027).CONCLUSION Of the 22 patients with pancreatic cancer, five(23%) experienced S-1 induced hepatic steatosis. Care should be taken during S-1 treatment of patients with pancreatic cancer.