Altered neurotransmission has been suggested to be a crucial factor in the pathophysiology of attention-deficit/hyperactivity disorder ADHD. Subsequently genes encoding for synaptic proteins have been investigated in candidate gene studies. These proteins mediate the release of neurotransmitters into the synaptic cleft in the process of signal transduction by forming a transient complex, enabling the junction of vesicle and synaptic membrane. One of the core proteins of this complex is the synaptosomal-associated protein 25 (SNAP25). It is one of the most validated candidate genes in ADHD according to meta-analyses. However, differing results were observed in previous studies, some of which were not able to observe association with ADHD. In this study we aimed to investigate association of genetic variants of SNAP25 located in the putative promoter region of SNAP25 and a SNP in intron 8, previously reported to associated with ADHD. A family based design was applied to detect preferential transmission of genetic variants. In our German ADHD sample no preferential transmission of either variant could be observed. Further investigation considering sub-sample analysis regarding response to D-amphetamine could enlight the role of SNAP25 in ADHD.