Background: Patterns of low heart rate, skin conductance and cortisol seem to characterise children with disruptive behaviour disorder (DBD). Until now, the startle paradigm has not been used in DBD children. We investigated whether DBD children, like adult psychopaths, process emotional stimuli in an abnormal way. Method: Twenty-one DBD and 33 normal control children viewed a series of 27 positive, neutral and negative slides. Startle probes were presented unpredictably during slide presentations and eye blink reflexes were measured. Results: DBD and control children showed a similar linear relationship between slide valence and startle magnitude, but the startle-elicited blinks of the DBD children were significantly lower for all categories of slides. Moreover, the more delinquent the DBD children were, the lower their startle responses during unpleasant states. Conclusions: The results suggest a deficit in neurophysiological fear modulation. The implications of the findings for the fearlessness theory of antisocial behaviour are discussed.