OBJECTIVES: The main goal of this study was to find the incidence of the dimethylacetamide (DMAc) induced toxic liver injury among workers who were exposed to DMAc for about 5 years in a synthetic fiber factory. METHODS: In our investigation, total 1,021 workers had been exposed to DMAc from 1st February, 2000 to 30th June, 2004. Among them, 24 workers who had initial abnormal hepatic enzyme level or was viral hepatitis B carrier were excluded. Finally, 997 DMAc exposed workers were followed up for their incidence of toxic liver injury. To find out DMAc induced toxic liver injury case, we carried out regular examinations including liver enzyme tests such as AST and ALT. RESULTS: We followed up 997 workers and among them 72 cases coincided with our case definition. Incidence density method was 6.05 per 100 person-year. and, a cumulative incidence by life table method was 0.0965 within a year. The incidence of the DMAc-induced toxic liver injury peaked at 4 to 5 in weeks after employment. There was no toxic liver injury case within second week after exposure to DMAc. Five new cases developed in 2th to 3th week, 25 cases in 4th to 5th week, 14 cases in 6th to 7th week, 12 cases in 8th to 9th week, 5 cases in 10th to 11th week, 4 cases in 12th to 13th week, 4 cases in 14th to 15th week, 1 case in 16th to 17th week, 1 case in 30th to 31th week, and there was one case in 48th to 49th week. CONCLUSIONS: The incidence rate of toxic liver injury was considerably high during the 1st year after a worker is placed. So it is needed to take careful monitoring of hepatic enzyme level for newly exposed worker.