Citalopram for Children With Autism and Repetitive Behavior (STAART Study 1)

Inclusion Criteria: * Able to walk * Diagnosis of Autistic Disorder, Asperger's Disorder, or PDD-NOS * Have a score greater than or equal to (\>) 8 on the sum of items 1A, 2, 3 and 5 of the Compulsions Subscale of the Revised CYBOCS. * Have a rating of at least moderate behavioral disturbance based on the modified Clinical Global Impression-Severity of Illness score (CGI-S) at the time of screening (See description below). * Be free of psychotropic medication for at least one month for fluoxetine, two weeks for other SSRIs and neuroleptics, and for 5 days for stimulants prior to baseline ratings. * Be judged reliable for medication compliance and agree to keep appointments for study contacts and tests as outlined in the protocol (both subject and guardian(s)). Exclusion Criteria: * Medical contraindications to therapy with SSRIs * Prior exposure to citalopram (or escitalopram) of sufficient dose or duration to determine response status * History of treatment failure to a clinically adequate trial of two select SSRIs * Diagnosis of Rett's Disorder or Childhood Disintegrative Disorder * Uncontrolled epilepsy, with a seizure within past 6 months * Child weighs less than (\<) 15 kg at screening contact. * Pregnancy * Presence of chronic medical conditions that might interfere with study participation or where study participation would be contraindicated * Clinically significant abnormal baseline laboratory testing * History of bipolar disorder or manic episode induced by antidepressant exposure * Documented need for ongoing psychotropic medications besides study medication (with the exception of stable dose (at least 3 month) anti-convulsants for seizures). * Concomitant medication that would interfere with participation in the study. * Recent (\< 2 months) initiation of behavior therapy (such as parent training, applied behavior analysis or behavior modification) in a clinic, with a private practitioner or in a school program. Participants who are in an established behavior therapy program (defined as greater than (\>) 2 months for clinic or private practitioner or greater than (\>) 1 month for school program) can be included in the study. Families will be asked not to initiate any new behavior therapy during the study.