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 described. 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 involved in medicolegal issues. Sexsomnia has some distinct features that separate it from sleepwalking. The automatic arousal is more prominent, motor activities are relatively restricted and specific, and some form of dream mentation is often present. CONCLUSIONS: A significant number of patients with this unusual parasomnia behaviour were identified only after specific questions were asked, suggesting that the behaviour is more common than previously thought.