• Functional Magnetic Resonance Imaging [ Time Frame: two 2-hr scans ] [ Designated as safety issue: No ]
  
• Clinicians Global Improvement Scale [ Time Frame: Upon study completion ] [ Designated as safety issue: No ]
  

• Childrens Yale-Brown Obsessive Compulsive Scale [ Time Frame: Baseline, wks 2, 4, 8, endpoint ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

• Ambulatory status (outpatient) at time of consent
• Age 10-55 years
• Clinical diagnosis of Autism Spectrum Disorder
• IQ greater than or equal to 70
• Score greater than 8 on Children's Yale-Brown Obsessive Compulsive Scale
• Free of psychoactive medication for at least: one month for fluoxetine; two weeks for other SSRIs and neuroleptics; and five days for stimulants prior to MRI scanning [excepting stable doses (greater than three months duration) of anticonvulsant medication for seizure disorder]

Exclusion Criteria:

• Age less than 10 years or greater than 55 years, at time of consent
• Estimated IQ < 70
• Uncontrolled epilepsy (seizure within 6 months prior to consent)
• 4. Presence of medical conditions that might interfere with participation, or where participation would be contraindicated
• History of neurological injury: head trauma, poorly-controlled seizure disorder (seizure within the preceding six months), stroke, prior neurosurgery, or under the care of a neurologist or neurosurgeon as determined by interview
• History of claustrophobia
• Implanted or irremovable metal in the body (including certain tattoos and permanent make-up)
• Current pregnancy (as verified by testing prior to both initial dose administration of citalopram or placebo and prior to magnetic resonance imaging) due to the risk that may be associated with SSRI treatment and magnetic resonance imaging on fetal health
• Medical contraindications to SSRI therapy as determined by history (including induction of mania or hypomania during SSRI therapy, or known drug allergy)
• Concomitant medication that would interfere with study participation
• Prior history of citalopram treatment failure at appropriate doses and duration
• Prior history of treatment failure to two previous SSRI trials at appropriate doses and duration
• Ongoing need for psychoactive medication other than study medication [excepting stable doses (greater than three months duration) of anticonvulsant medication for seizure disorder, or diphenhydramine (Benadryl®)for sleep]