A functional length variation in the transcriptional control region of the serotonin transporter gene (5-HTTLPR) influences brain function, personality traits, and susceptibility to psychiatric disorders. Here we measured prefrontal brain function by means of event-related potentials during an error processing paradigm. Physiologically, occurrence of an error elicits two specific electrical responses in the prefrontal cortex, the early error related negativity (Ne/ERN) and the later occurring error positivity (Pe), reflecting different components of error processing. Healthy subjects with one or two copies of the low-activity 5-HTTLPR short variant showed significantly higher amplitudes of the Ne/ERN and a trend to higher amplitudes of the Pe as compared to age- and gender-matched individuals homozygous for the long allele. Performance measures and latencies of these ERP-components did not differ between groups. These results indicate that the 5-HTTLPR short variant is associated with enhanced responsiveness of the brain and further supports the notion that prefrontal brain function is influenced by allelic variation in serotonin transporter function.