According to the mental health professional's handbook, Diagnostic and Statistical Manual of Mental Disorders , two criteria are required to make a diagnosis of voyeurism:
Over a period of at least six months, an individual must experience recurrent, intense, sexually arousing fantasies, sexual urges, or behaviors that involve the act of observing an unsuspecting person who is naked, in the process of disrobing, or engaging in sexual activity.
The fantasies, sexual urges, or behaviors must cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.
In order for a condition to be labeled "voyeurism," the fantasies, urges, or behaviors to watch other persons must cause significant distress in the individual or be disruptive to his or her everyday functioning.
Read more: http://www.minddisorders.com/Py-Z/Voyeurism.html#ixzz3raEjK9F0