Obsessive-compulsive disorder (OCD) is an anxiety disorder that is associated with recurring repetitive behaviors and persistent unwanted thoughts. People with OCD often carry out ritual-like behaviors such as counting, cleaning, or washing their hands in order to momentarily ease their anxiety. A current treatment for people with OCD is the class of antidepressants called selective serotonin reuptake inhibitors (SSRIs). A recent re-analysis of clinical trials on children with psychiatric conditions found that the risk of suicidal thoughts and behavior when on SSRI-antidepressants was considerably higher than when on placebo. The data also revealed that antidepressant-associated suicidal behavior was not limited to children with depression, but also affected children with OCD and other anxiety disorders. Although the process responsible for increased suicidality is unknown, it may be initiated by a set of symptoms collectively called SSRI induced activation syndrome, which is thought to be common, particularly in children and teens. However, there is a lack of knowledge on this syndrome, including its role in suicidal behavior and how it can be prevented. This study will evaluate a new behavioral test to measure certain side effects linked to antidepressant use. This study will also evaluate the effectiveness of the SSRI sertraline plus cognitive behavioral therapy (CBT) to treat people with OCD.