The aim of this study was to analyse the relationship between work in an operating room and pregnancy outcome, as described by the rates of spontaneous abortion and of birth defects. The population comprised the female nurses of 17 hospitals in Paris, interviewed in 1987-1989. An exposed group included all operating room nurses, and a control group was composed of female nurses in other departments matched by hospital, age and duration of service. Each woman described all prior pregnancies. In total, 776 pregnancies were described by 418 nurses who were first pregnant in 1970 or thereafter; ectopic pregnancies, those terminated by voluntary induced abortion and those leading to multiple births were excluded. The rate of spontaneous abortion was significantly higher for pregnancies during which women worked in an operating room than for the other pregnancies. Birth defects were not significantly related to work in an operating room during pregnancy. These results are in agreement with others showing a significant relationship between occupational exposure to operating rooms and spontaneous abortion, although identification of the responsible factor remains difficult. They suggest that effective ventilating systems should be installed in all operating rooms and that special preventive measures must be taken for women of childbearing age.