Objective: To assess the potential efficacy, tolerability, and safety of citalopram in the treatment of functional pediatric recurrent abdominal pain and comorbid internalizing disorders. Method: Twenty-five clinically referred children and adolescents with recurrent abdominal pain aged 7 to 18 years, inclusive, participated in a 12-week, flexible-dose, open-label trial of citalopram. Primary outcome measure was the Clinical Global Impression Scale-Improvement, with responders defined by ratings of 1 (very much improved) or 2 (much improved). Secondary measures included self- and parent reports of abdominal pain, anxiety, depression, other somatic symptoms, and functional impairment. Side effects were assessed using a standardized checklist. Data were analyzed using an intent-to-treat format and the last observation carried forward procedure. Results: Twenty-one subjects (84%) were classified as responders (Clinical Global Impression Scale-Improvement score [less than or equal to]2). Citalopram was generally well tolerated. Four subjects withdrew prematurely, one due to reported visual side effects. Ratings of abdominal pain, anxiety, depression, other somatic symptoms, and functional impairment all improved significantly over the course of the study compared with baseline. Conclusions: Citalopram is a promising treatment for functional pediatric recurrent abdominal pain and deserves additional study with a randomized, placebo-controlled clinical trial. J. Am. Acad. Child Adolesc. Psychiatry, 2004;43(10):1234-1242. Key Words: abdominal pain, anxiety, depression, comorbidity, serotonin.