We used National Fragile X Survey data in order to examine reported self-injurious behavior (SIB) to (a) generate lifetime and point prevalence estimates, (b) document detailed features of SIB (frequency, types, location, severity) in relation to gender, and (c) compare comorbid conditions between matched pairs (SIB vs. no SIB). Results indicate significant gender differences in frequency, topography, and location of SIB as well as sleep difficulties, comorbid conditions, pain sensitivity, and seizures. Matched pair comparisons (SIB vs. no SIB) revealed differences for males in sensory and attention problems, hyperactivity, aggression, autism, and anxiety and for females, in autism, attention, and anxiety. These results further clarify gender differences as well as comorbidity patterns between children with fragile X syndrome with and without SIB.