The diagnostic value of a test depends on the variability of the test results and the accuracy of the test. The object of this investigation was to estimate the observer variability and the accuracy, when intrapartum CTGs were assessed by experienced obstetricians. Fifty CTGs were evaluated twice by four obstetricians. They were asked to identify the CTGs belonging to the compromised infants. They were told the criteria for a compromised infant and the incidence (one-third). Eleven (22%) of the CTGs were assessed in the same way of all the obstetricians in both evaluations. Between the obstetricians, the accuracy ranged from 50 to 66%. We conclude that the considerable observer variability found in this and other investigations must severely impair the clinical value of electronic fetal monitoring (EFM). The variability must be reduced before the "true" predictive value and the cost/benefit of EFM can be estimated.