The present study describes an investigation on the use and management of ethylene oxide (EO) which is used mainly as a sterilant in medical institutions in a Cabinet-order designated city. Information was obtained from a self-administered questionnaire on safety and health matters related to sterilization with EO gas. The questionnaire was sent to 189 medical institutions including major hospitals and randomly selected clinics. 127 questionnaire were returned and the analysis was carried out for 120 respondents, excluding seven respondents whose answers were found to be inappropriate. The proportion of medical institutions, employing more than 50 workers, in which an occupational health physician and/or health supervisor was appointed was 70% and was lower than for other industries. 1.6% of the employees engaged in EO sterilization activities in the hospitals, whereas in clinics the percentage was as high as 20%. Several problems were found both in the management and work methods with EO: operations were not isolated in 46%; gas leaks and back-streaming of exhaust gas were found in 59% and 41%, respectively; and personal protective clothing was not used in 69%. Improvement was found only for three items among the institutions where an occupational health physician was appointed. These results suggest that good workplace controls and practices are essential for medical institutions using hazardous materials including EO for sterilization.