The search for a genetic vulnerability gene for substance abuse has focused on dopaminergic genes, including the DRD4 receptor. In addition to clear biological mechanisms in substance abuse, many studies have found a psychological attentional bias to drug-related stimuli in substance users. This study aimed to determine whether a DRD4 gene polymorphism is associated with such attentional biases to substance-related stimuli. Eighty heroin abusers in treatment, 80 cigarette smokers, 80 alcohol abusers in treatment and 80 non-smoking community controls undertook an emotional Stroop task to measure attentional bias to drug-related stimuli. DNA was obtained from cheek cell samples and the DRD4 VNTR polymorphism genotyped. Heroin abusers and cigarette smokers, but not controls, who carried the long variant at the DRD4 gene spent significantly longer responding to drug-related stimuli than they did to neutral stimuli when compared to those who did not carry the long variant at the DRD4 gene. A non-significant trend to delay was observed in alcoholics. These findings suggest that variants at the DRD4 gene influence attentional bias in substance abusers and offer further insight into the role of the DRD4 gene in drug dependence as well as individual differences in the susceptibility to attentional bias to drug-related environmental cues.