Introduction: The synaptosomal-associated protein of 25 kDa (SNAP-25) gene is a presynaptic plasma membrane protein and an integral component of the vesicle docking and fusion machinery mediating secretion of neurotransmitters (1). Previously, several studies reported association between SNAP-25 and attention deficit hyperactivity disorder (ADHD) (2). We investigated whether these SNAP-25 polymorphisms (Mn1I T/G and Ddell T/C) were also associated with ADHD in the Turkish population. Method: Our study comprised unrelated 79 subjects who met DSM-IV criteria for ADHD and 73 controls and all were of Turkish origin. Genetic analyses were performed and patients were evaluated with Wender-Utah and Turgay rating scales. Results: SNAP-25 Ddell polymorphism was not associated with ADHD but there was a statistically significant difference between ADHD patients and controls for SNAP-25 Mn1I polymorphism (p<0.05). For SNAP-25 Mn1I polymorphism patients with GG genotype had higher average of Wender-Utah and Turgay scores than patients with TT and TG genotype. Conclusion: We detected a significant association of the MnIl polymorphism in our ADHD sample which was similar to previous findings (2). Our study also revealed that SNAP-25 Mn1I polymorphism was also associated with symptom severity of ADHD. This study is also, the first report on the association of SNAP-25 with ADHD in the Turkish population.