The Behavior Flexibility Rating Scale (BFRS) is designed to assess insistence on sameness or lack of behavioral flexibility, which is often associated with autism and other developmental disabilities. This study was designed to assess the factor structure of this scale for a sample of 968 individuals with autism, Asperger's syndrome, and Down syndrome. To establish factorial validity, an exploratory factor analysis (EFA) was conducted with half of the sample, with a confirmatory factor analysis (CFA) conducted with the remaining cases to cross-validate the model obtained with the EFA. The factor analyses supported the presence of two factors--Interruption/Disruption and Position/Location. However, further analysis suggested the presence of a third factor, Interpersonal Mishaps, for the Asperger's syndrome group.