The purpose of this study is to find out if D-Cycloserine (DCS), taken at the same time as a child gets cognitive behavioral therapy (CBT) can help children with pediatric obsessive-compulsive disorder.

Cognitive Behavior Therapy is a talking therapy that will teach children new skills to better cope with his/her OCD. CBT usually uses "exposure-based therapy". This means that the person with OCD slowly learns to deal with things they usually avoid. This is done by moving from less stressful situations to more challenging ones.

The investigators hope to enroll about 75 children ages 7-17 years old with OCD in this study at Massachusetts General Hospital (MGH). The National Institute of Mental Health (NIMH) is paying for this study to be done.

If your child qualifies for the study, the investigators will assign him or her by chance (like a coin toss) to either the DCS group or the placebo group. You and the study doctor cannot choose your child's study group. Your child will have an equal chance (1 in 2) of being assigned to the DCS group.

Your child will be asked to take one or two capsules of the study drug (either DCS or placebo, depending which study group they were assigned to) one hour before CBT visits 4-10. The study coordinator will give your child the study drug at the location of the CBT sessions. This is to make sure that your child takes the study drug one hour before his/her scheduled therapy session. We will ask you to record any bad side effect from the study drug that your child may have before each CBT session.

It will take your child about 34 weeks to complete the study. During this time, the investigators will ask you and your child to make a minimum of 17 trips to the study center. There may be up to 23 trips when including CBT Booster sessions.

This study uses a placebo. The placebo looks exactly like the DCS, but it contains no DCS. The investigators use placebos in research studies to learn if the the results are caused by the study drug or are due to other reasons. This is a double-blind study. A double-blind study is a study where both the doctor and the study participant do not know whether the study participant is being given DCS or placebo.

Inclusion Criteria:

• Clinical diagnosis of Obsessive-Compulsive Disorder as primary or co-primary diagnosis
• Score on CY-BOCS of 16 or greater
• Full Scale IQ greater than or equal to 85
• English speaking

Exclusion Criteria:

• Receiving concurrent psychotherapy or a past adequate trial of CBT for OCD
• Initiation of an antidepressant within 12 weeks before study enrollment
• Initiation of an antipsychotic within 6 weeks before study enrollment
• No new alternative medications, nutritionals, or therapeutic diets within 6 weeks of study enrollment
• Any change in established psychotropic medication within 8 weeks before study enrollment (6 weeks for antipsychotic). Alternative medications must be stable for 6 weeks prior to baseline. Any medications must remain stable during treatment.
• Current clinically significant suicidality
• Suicidal behaviors within six months
• DSM-IV conduct disorder
• DSM-IV autism
• DSM-IV bipolar
• DSM-IV schizophrenia or schizo-affective disorders
• Substance abuse within the past six months
• Hoarding symptoms (due to difficulty implementing E/RP tasks)
• Weight less than 22.5k
• Epilepsy or renal insufficiency
• Current and/or past history of alcohol abuse (DCS is contraindicated)
• Pregnant or having unprotected sex (in females)
• Presence of a significant and/or unstable medical illness that might lead to hospitalization during the study
• Known DCS allergy

206 subjects were initially enrolled at MGH and USF. Of those, 32 were considered screen fails and 32 were not randomized either because they did not meet inclusion or exclusion criteria at randomization or because they withdrew consent or dropped out. Thus, 142 participants were randomized.