Fragile X syndrome is the most common inherited cause of intellectual and developmental disability. The influence of environmental variables on behaviors associated with the syndrome has received only scant attention. The current study explored the function served by problem behavior in fragile X syndrome by using experimental functional analysis methodology with 8 children with fragile X. No child met criteria for attention-maintained problem behavior, 5 children met criteria for escape-maintained problem behavior, and 4 children met criteria for tangible-maintained problem behavior. Results are discussed and compared with previous findings on the function of problem behavior in fragile X syndrome, and implications for intervention are discussed. It is noted that the external validity of these findings is limited by the small sample size.