The present study examined the startle reflex as a physiological marker of behavioral inhibition. Participants were 7 to 12-year-old children who had been previously identified as inhibited or uninhibited as part of an ongoing longitudinal study on the role of behavioral inhibition in the development of anxiety disorders. Analysis of their scores on the Behavioral Inhibition Scale revealed that the children were stable in their behavioral inhibition categorization as compared to the beginning of the longitudinal study. An experiment was carried out to study startle modulation effects in response to novel and familiar pictures of threatening and non-threatening facial expressions in inhibited and uninhibited children. The main results can be summarized as follows. To begin with, no modulation effect was found. That is, children did not show the expected (adult-like) startle facilitation while viewing unpleasant pictures. Second, a habituation effect was found: that is, during the testing phase children responded more intensely to the first block of slides than to the second block of slides (irrespective of slide content). Third, unexpectedly behaviorally inhibited children displayed smaller eye blink magnitudes in response to novel slides than uninhibited children. Fourth and finally, no meaningful differences were found in the patterns of startle responses of both genders. (Contains 2 figures.)