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Parasomnias are well-described, common nocturnal phe-nomena. By definition, parasomnias are “events that oc-cur intermittently or episodically during the night ” (1,2). They may occur in any phase of sleep. Most parasomnias are char-acterized by partial arousals before, during, or after the event. There are several classifications of the major parasomnias—a widely used description of the types of parasomnias is pro-vided in DSM-IV (3) and the International Classification of Sleep Disorders (4). New additions are expected to enter the International Classification, for example, the newly described disorder of sleep eating (5) and overlap parasomnias (6). While parasomnias are considered normal in children, where the prevalence is relatively high (> 15%), in adults they may be indicative of a psychopathology, and the prevalence is rela-tively low (> 6%) (7). The most common precipitants of parasomnic behaviour in adults are stress, sleep deprivation, and alcohol or drug consumption. It is common for family members to have similar parasomnias. Can J Psychiatry, Vol 48, No 5, June 2003 311 Objective: To describe a distinct parasomnia involving sexual behaviour, which we have named sexsomnia. Method: We have used a case series as a basis for the description of sexsomina. Results: Eleven patients with distinct behaviours of the sexual nature during sleep are de-scribed. The features in common with other nonrapid eye movement arousal parasomnias, such as sleepwalking are documented. Some patients had simply been referred to a tertiary sleep clinic for investigation of unrelated sleep problems. A small number had been in-volved in medicolegal issues. Sexsomnia has some distinct features that separate it from sleepwalking. The automatic arousal is more prominent, motor activities are relatively re-stricted and specific, and some form of dream mentation is often present. Conclusions: A significant number of patients with this unusual parasomnic behaviour were identified only after specific questions were asked, suggesting that the behaviour is more common than previously thought