History Taking: A doctor will note down all symptoms including behaviour and frequency of symptoms, and consider if there is a family history of OCD. This is done not only to establish a positive diagnosis, but also to rule out other conditions.
Evaluation: A doctor should tactfully establish if a particular symptom is only by habit or obsession. Symptoms should be of sufficient intensity as to disrupt normal life of patient.
Mental Health Assessment Test: A list of carefully drawn questionnaires will help to establish diagnosis.
Child OCD: It is difficult to diagnose OCD in a child because children usually do not realize if they have a condition, and they appear confused on questioning. A gentle approach, knowledge of OCD and circumspection is necessary.