According to the ICD-10 (WHO, 1992), for a diagnosis of OCD, obsessional symptoms or compulsive acts, or both, must be present on most days for at least 2 successive weeks and be a source of distress or interference with activities.
The obsessional symptoms must be recognized as the individual’s own thoughts or impulses and there must be at least one thought or act that is still resisted unsuccessfully, even though others may be present which the sufferer no longer resists. In addition, the thought of carrying out the act must not in itself be pleasurable and the thoughts, images, or impulses must be unpleasantly repetitive.
The majority of compulsive acts are concerned with cleaning, repeated checking to ensure that a potentially dangerous situation has not been allowed to develop, or orderliness and tidiness. Underlying the overt behaviour is a fear, usually of danger either to or caused by the patient, and the ritual act is an ineffectual or symbolic attempt to avert that danger. Compulsive ritual acts may occupy many hours every day and are sometimes associated with marked indecisiveness and slowness
Click here for the full NICE CG31 (November 2005) guidelines for OCD.