Complex phenotypes such as performance on the continuous performance test (CPT) are likely to exhibit epistasis. Genetic polymorphisms of noradrenergic system and brain-derived neurotrophic factor (BDNF), which participates in the differentiation and survival of noradrenergic neurons, have been reported to be associated with the performance on CPT. We evaluated the effect of the adrenergic α-2A receptor (ADRA2A) and BDNF gene–gene interaction on performance on the CPT in a Korean population with attention-deficit/hyperactivity disorder. In all, 122 participants with attention-deficit/hyperactivity disorder (8.6±2.3 years, 104 boys and 18 girls) completed the CPT. The DraI polymorphism of ADRA2A (rs583668) and rs11030101 polymorphism of BDNF were genotyped. Significant interaction effect was found of ADRA2A rs553668 and BDNF rs11030101 on response time variability (P=0.011) of the CPT. Our study provides preliminary evidence for the effect of the BDNF and ADRA2A gene–gene interaction on performance on the CPT in attention-deficit/hyperactivity disorder.