Both behavioral and pharmacological treatments have been used to treat repetitive and stereotyped behaviors in autism. Behavioral treatments include the use of noncontingent reinforcement (Britton, et al., 2002) and alternative response training to maintain homeostasis (Johnson, Laarhoven, & Repp, 2002). Psychopharmacological approaches include the use of SSRIs given the similarity between repetitive behaviors in autism and OCD (McDougle, 1995) and evidence for serotonin dysfunction in ASD (Hollander, 2000). To date, there are few controlled studies with any of the SSRIs in pediatric populations with ASD. Hollander & colleagues (Hollander, et al., in press) at Mt. Sinai recently completed a study suggesting the efficacy of low-dose liquid fluoxetine on reducing repetitive behaviors in a double-blind, placebo controlled crossover study of 45 children with ASD. This proposed FBA evaluation would occur within another SSRI trial at Mt. Sinai, which aims to extend previous findings in a large scale, multisite investigation of the safety and efficacy of liquid citalopram in children with ASD.