The American Psychiatric Association has classified certain voyeuristic fantasies, urges and behaviour patterns as a paraphilia in the Diagnostic and Statistical Manual (DSM-IV) if the person has acted on these urges, or the sexual urges or fantasies cause marked distress or interpersonal difficulty. It is described as a disorder of sexual preference in the ICD-10. The DSM-IV defines voyeurism as the act of looking at "unsuspecting individuals, usually strangers, who are naked, in the process of disrobing, or engaging in sexual activity". The diagnosis would not be given to people who experience typical sexual arousal simply by seeing nudity or sexual activity. In order to be diagnosed with voyeuristic disorder the symptoms must persist for over six months and the person in question must be over the age of 18.
There is relatively little academic research regarding voyeurism. When a review was published in 1976 there were only 15 available resources. Voyeurs were well-paying hole-lookers in especially Parisian brothels, a commercial innovation described as far back as 1857 but not gaining much notoriety until the 1880s, and not attracting formal medical-forensic recognition until the early 1890s. Society has accepted the use of the term voyeur as a description of anyone who views the intimate lives of others, even outside of a sexual context. This term is specifically used regarding reality television and other media which allow people to view the personal lives of others. This is a reversal from the historical perspective, moving from a term which describes a specific population in detail, to one which describes the general population vaguely.
One of the few historical theories on the causes of voyeurism comes from psychoanalytic theory. Psychoanalytic theory proposes that voyeurism results from a failure to accept castration anxiety and as a result a failure to identify with the father.
Voyeurism has high prevalence rates in most studied populations. Voyeurism was initially believed to only be present in a small portion of the population. This perception changed when Alfred Kinsey discovered that 30% of men prefer coitus with the lights on. This behaviour is not considered voyeurism by today's diagnostic standards, but there was little differentiation between normal and pathological behaviour at the time. Subsequent research showed that 65% of men had engaged in peeping, which suggests that this behaviour is widely spread throughout the population. Congruent with this, research found voyeurism to be the most common sexual law-breaking behaviour in both clinical and general populations. In the same study it was found that 42% of college males who had never been convicted of a crime had watched others in sexual situations. An earlier study indicates that 54% of men have voyeuristic fantasies, and that 42% have tried voyeurism. In a national study of Sweden it was found that 7.7% of the population (both men and women) had engaged in voyeurism at some point. It is also believed that voyeurism occurs up to 150 times more frequently than police reports indicate. This same study also indicates that there are high levels of co-occurrence between voyeurism and exhibitionism, finding that 63% of voyeurs also report exhibitionist behaviour.
Due to the prevalence of voyeurism in society, the people who engage in voyeuristic behaviours are diverse. However, there are some trends regarding who is likely to engage in voyeurism. These statistics apply only to those who qualify as voyeurs under the definition of the DSM, and not the broader modern concept of voyeurism as discussed earlier in this article.
Early research indicated that voyeurs were more mentally healthy than other groups with paraphilias. Compared to the other groups studied, it was found that voyeurs were unlikely to be alcoholics or drug users. More recent research shows that, compared to the general population, voyeurs were moderately more likely to have psychological problems, use alcohol and drugs, and have higher sexual interest generally. This study also shows that voyeurs have a greater number of sexual partners per year, and are more likely to have had a same-sex partner than general populations. Both older and newer research found that voyeurs typically have a later age of first sexual intercourse. However, other research found no difference in sexual history between voyeurs and non-voyeurs. Voyeurs who are not also exhibitionists tend to be from a higher socioeconomic status than those who do show exhibitionist behaviour.
Research shows that, like almost all paraphilias, voyeurism is more common in men than in women. However, research has found that men and women both report roughly the same likelihood that they would hypothetically engage in voyeurism. There appears to be a greater gender difference when actually presented with the opportunity to perform voyeurism. There is very little research done on voyeurism in women, so very little is known on the subject. One of the few studies deals with a case study of a woman who also had schizophrenia. This limits the degree to which it can generalise to normal populations.
Lovemap theory suggests that voyeurism exists because looking at naked others shifts from an ancillary sexual behaviour, to a primary sexual act. This results in a displacement of sexual desire making the act of watching someone the primary means of sexual satisfaction.
Voyeurism has also been linked with obsessive–compulsive disorder (OCD). When treated by the same approach as OCD, voyeuristic behaviours significantly decrease.
Historically voyeurism has been treated in a variety of ways. Psychoanalytic, group psychotherapy and shock aversion approaches have all been attempted with limited success. There is some evidence that shows that pornography can be used as a form of treatment for voyeurism. This is based on the idea that countries with pornography censorship have high amounts of voyeurism. Additionally shifting voyeurs from voyeuristic behaviour, to looking at graphic pornography, to looking at the nudes in Playboy has been successfully used as a treatment. These studies show that pornography can be used as a means of satisfying voyeuristic desires without breaking the law.
Voyeurism has also been successfully treated with a mix of anti-psychotics and antidepressants. However the patient in this case study had a multitude of other mental health problems. Intense pharmaceutical treatment may not be required for most voyeurs.
There has also been success in treating voyeurism through using treatment methods for obsessive compulsive disorder. There have been multiple instances of successful treatment of voyeurism through putting patients on fluoxetine and treating their voyeuristic behaviour as a compulsion.