The outcome of deliveries during 1973 and 1975 of women working during their pregnancy in operating rooms, using register data that provided information on both occupation and outcome of delivery was studied. There were 494 women who worked throughout pregnancy, 37 women worked for more than half of their pregnancies, and 10 women worked during less than half of their pregnancies. The study groups were compared with a reference population composed of all women employed in medical work in Sweden who were delivered during the 2 years. The study population differed from the reference population with respect to maternal age (and perhaps also to parity); corrections were made for this. No differences in the incidence of threatened abortions, in birth weight, in perinatal death rate, or in the incidence of congenital malformations were found. Possibly more gestations lasting less than 37 weeks were noted. We suggest that the negative outcome of the study is due to the unbiased data collection.