Using national data, we examined emergency department (ED) encounters during 2006-2011 for which a diagnosis code for fragile X syndrome (FXS) was present (n = 7,217). Almost half of ED visits coded for FXS resulted in hospitalization, which is much higher than for ED visits not coded for FXS. ED visits among females coded for FXS were slightly more likely to result in hospitalization. These findings underscore the importance of surveillance systems that could accurately identify individuals with FXS, track healthcare utilization and co-occurring conditions, and monitor quality of care in order to improve care and reduce FXS-associated morbidity.