Paraphilias are abnormal sexual urges, fantasies or behaviors that are recurrent and intense. They usually first occur in adolescence and last a lifetime. They may occur at any time or just recur periodically, especially during periods of stress. Sexual arousal for people with paraphilias most often involves unwilling participants (including children), inanimate objects, animals, or suffering and humiliation.

The focus of sexual arousal differs, depending on the type of paraphilia. The most commonly diagnosed paraphilias are those that involve criminal behavior and may only be diagnosed after the patient has been apprehended. These include pedophilia (sexual attraction to children), sexual exhibitionism (exposing or "flashing" one’s own genitals for sexual gratification), voyeurism (viewing the nudity or sexual activity of unsuspecting people, or "peeping") and frotteurism (rubbing one’s genitals against strangers).

Many other types of paraphilias exist. Sources of sexual excitement can include articles of clothing, pain, specific body parts (e.g., feet), urine, feces, enemas and animals. Patients with a paraphilia often have more than one type.

It is difficult to identify signs of paraphilias or to know how common they are. Many people with paraphilias do not seek help for their behavior and they engage in the behavior in private. Consensual sexual activity among adults may encompass a wide range of behavior and may not be considered paraphilia. Paraphilias are believed to be more common than currently reported.

Nearly all patients with paraphilias are male and half of all people in treatment for a paraphilia are married, according to the American Psychiatric Association (APA). Although the cause of paraphilias is unknown, people with childhood sexual abuse or early exposure to deviant sexual behavior may have a greater risk of developing paraphilias.

The first step in identifying a paraphilia is a mental health evaluation. A person needs to meet specific criteria established by the APA for diagnosis of a paraphilia.

Some patients with paraphilias also have personality, mood, anxiety or eating disorders. In addition, they may be subject to consequences of paraphilias, including arrest, physical injury, sexually transmitted diseases, interpersonal difficulties, depression and sexual dysfunction.