Inclusion Criteria:

• At least 3 episodes of abdominal pain during the previous 3 months associated with functional impairment in the absence of explanatory physical disease following clinically appropriate medical assessment.
• Age 7 years 0 months to 18 years 11 months, inclusive, at initial evaluation.
• Significant global functional impairment as reflected by a score less than 70 on the Children's Global Assessment Scale
• Residing with a primary caretaker (i.e., parent, legal guardian, relative functioning as a parent, or foster parent) who has known the child well for at least 6 months prior to study entry and has legal authority to consent to participation.

Exclusion Criteria:

• Physical disease sufficient to explain the subjective distress and functional impairment suffered by the subject.

• FAP with atypical features:

  1. Abnormal abdominal or rectal examination
  2. GI bleeding (i.e., hematest positive stool or hematemesis)
  3. History of recurrent or persistent fever associated with the abdominal pain
  4. Involuntary weight loss (> 5% of body weight) over the previous 3 months
  5. Previous laboratory evidence suggesting explanatory physical disease
  6. Persistent nighttime awakenings due to abdominal pain (at least once per week and > 4 per month)
  7. Persistent or bilious vomiting (at least once per week and > 4 per month)
  8. Abdominal pain exclusively associated with menstruation
  9. Dysuria
• Physical disease in which citalopram monotherapy or study participation might prove to be disadvantageous or incompatible with quality care, including bleeding disorder characterized by prolonged bleeding time, uncontrolled epilepsy, or poorly controlled diabetes mellitus.
• Psychiatric problem or disorder in which citalopram monotherapy or study participation might prove to be disadvantageous or incompatible with quality care, including evidence that the child is a serious acute danger to self or others, anorexia nervosa, bulimia nervosa, schizophrenia, schizoaffective disorder, alcohol or substance abuse/dependence, or bipolar disorder.
• History of mental retardation as defined by full scale IQ < 70 on previous testing or participation in special education placement for mild to severe mental retardation.
• Inadequate English speaking abilities of child or parent(s) to complete study measures and/or communicate with study examiners.
• Adequate prior trial of citalopram, escitalopram, or another selective serotonin reuptake inhibitor or venlafaxine. Adequate trial is defined as at least 4 weeks of citalopram 20 mg/day, escitalopram 10 mg/day, fluoxetine 20 mg/day, fluvoxamine 100 mg/day, paroxetine 20 mg/day, sertraline 50 mg/day, or venlafaxine 75 mg/day.
• Concurrent use of non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, or anticoagulant medications.
• Treatment for physical or psychiatric illness initiated within the prior 4 weeks or escalating in dosage or intensity.
• History of hypersensitivity to citalopram or serotonin-syndrome.
• Participation in any investigational drug study within thirty days of study entry.
• Pregnancy
• Sexually active female subjects refusing to use a medically accepted method of birth control during the study, or who engaged in unprotected sexual activity during the 30 days prior to the study.