Duhaime's Law Dictionary

Penile Plethysmograph Definition:

A law investigation device which purports to measures the reaction of a target's penis to visual stimuli.

Related Terms: Polygraph

A law enforcement and investigation tool used to identify the sexual attraction of sex offenders, their treatment and monitoring or as a monitoring tool in the context of parole.

Penile cuffs are attached to a pulse volume recorder (plethysmograph) that displays and can record waves of blood to the penis during photographic or such other visual, or even audio stimuli.

One law journal, the US Air Force's JAG's The Reporter, offered this:

"A penile plethysmograph is a biofeedback device developed in the 1950s. It is generally used to measure the engorgement of the male sex organ in conjunction with the administration of auditory and/or visual stimuli.

"The results of penile plethysmograph testing may be proffered by the defense in courts martial in an attempt to prove that the accused is not a sex offender, or that his potential for recidivism is very low....

"(T)he use of the penile plethysmograph as a predictive or forensic tool fails to meet the relevant legal standards for admissibility and has been repeatedly rejected by the scientific community."

In 200, Canada's Supreme Court used these words in R. v. J.-L.J.:

"The penile plethysmograph ... is generally recognized by the scientific community and is used by psychiatric facilities ... to monitor the result of treatment for sexual pathologies. The plethysmograph enables the medical staff to assess the progress of therapy of known and admitted sexual deviants.....

"A level of reliability that is quite useful in therapy because it yields some information about a course of treatment is not necessarily sufficiently reliable to be used in a court of law to identify or exclude the accused as a potential perpetrator of an offence. In fact, penile plethysmography has received a mixed reception in Quebec courts."

In US v Powers, Justice Williams of the United States Court of Appeals concluded that there was "... extensive, unanswered evidence weighing against the scientific validity of the penile plethysmograph test" in agreeing with the proposal that:

"... the scientific literature addressing penile plethysmography does not regard the test as a valid diagnostic tool because, although useful for treatment of sex offenders, it has no accepted standards in the scientific community."

In their December 2012 article in Cardiff University Law School's Law and Society Journal, Andrew S. Balmer and Ralph Sandland wrote

"(A) penile plethysmograph ... is a device designed to measure changes in sexual arousal by one of two methods: a volumetric air chamber can be placed over the subject's penis, this measures the swelling that occurs as a result of increased blood volume; or a circumferential transducer, in essence a rubber ring, is placed around the penis to measure changes in circumference. Whilst this apparatus is in place, sex offenders may be exposed to visual images or auditory descriptions of different types of sexual activity with various types of partner. Images of real children have been used and may still be in use but it has become taboo; the use of computer-fabricated images of children and adults appears to be more acceptable now."



  • Balmer, A. and Sandland, R., Making Monsters: The Polygraph, the Plethysmograph, and Other Practices for the Performance of Abnormal Sexuality, 39:4 JLS 593–615 (2012)
  • Mathews, C., Hartsell, J. and Kohn, Maureen, Debunking Penile Plethmograph Evidence, 28 Reporter 11 (2001)
  • R. v. J.-L.J., 2000 SCC 51
  • US v. Powers, 59 F. 3d 1460 (1995)

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