A system was developed for continuous, full-night, polysomnographic recording of sleep using manual sleep scoring and automatic electromyographic analysis of craniomandibular muscle activity. In the sleep laboratory, data are stored on tape with hard copy on paper followed by off-line, computer-controlled digital processing. Muscle activity is described by the Amplitude Probability Distribution Function and by parameters of time and intensity. Sleep and electromyographic data are available graphically on screen, and the results are presented in tables and graphics after statistical treatment. The system was developed to provide a differentiated, detailed analysis of sleep and nocturnal muscle activity in the craniomandibular system that is suitable for comparing groups of individuals, effects of treatments, and physical load of muscles. Applications of the system are demonstrated.