Fragile X syndrome is the most frequent cause of familial mental retardation and the second most common overall cause of mental retardation after Down syndrome. Clinical features of fragile X syndrome vary widely, and include cognitive, behavioral, and morphologic signs and symptoms. Fragile X mental retardation protein (FMRP) plays a number of crucial roles in dendritic maturation and function. The most common seizure type seen in fragile X syndrome is complex partial and the most common electroencephalogram (EEG) pattern is centrotemporal spikes. The definitive diagnosis of fragile X syndrome is made by genetic testing and requires an alteration in the FMR1 gene which can be detected by polymerase chain reaction (PCR) or Southern blot analysis. The treatment of individuals with fragile X syndrome is mainly symptomatic and ideally involves a multidisciplinary team to address common comorbidities including anxiety, behavioral problems, attentional difficulties, and other psychiatric disorders.