Down regulation of serotonin transporter (5-HTT) expression has been associated with brain function and major depression. The aim of this study was to explore the allelic variation (short and long) of the 5-HTTLPR polymorphism in attention bias associated with top-down processing of emotion. One hundred sixty-two healthy participants underwent genotyping (5-HTTLPR), background interviews, psychological screening, and a computerised test session (The Emo 1-back task). Carriers of the short 5-HTTLPR alleles in the serotonin transporter gene (SLC6A4) demonstrated less accuracy in The Emo 1-back task when presented with successive images of sad or fearful faces, but not for happy or neutral emotional faces. The study suggests an association between 5-HTTLPR variation in the serotonin transporter gene and altered emotion processing.