It was aimed to investigate the association of the synapsin III gene -196 G> A and -631 C>G polymorphisms that takes place in an encoding presynaptic protein, with adult attention deficit hyperactivity disorder (ADHD). One hundred thirty-nine patients having adult ADHD and 106 controls were included in the study. DNA samples were extracted from whole blood and genetic analyses were performed. A significant difference was determined between ADHD and synapsin III gene -631 C>G polymorphism compared to the control group. No significant difference was determined between ADHD and synapsin III gene -196 G>A polymorphism. These polymorphisms were found not to be associated with subtypes of ADHD. It is supposed that synaptic protein genes together with dopaminergic genes might have roles in the etiology of ADHD.