Some non-rapid eye movement (NREM) parasomnias, such as sleep-walking (SW), sleep terror (ST) and, in some aspects, sleep enuresis (SE), are considered "arousal disorders" without significant polysomnographic changes in classic sleep macrostructure. The aim of our study was to evaluate sleep microstructure and oscillations of arousal level by cyclic alternating pattern (CAP) scoring in some NREM parasomnias. Nocturnal polysomnography and videotape recording was used to study 21 patients with motor and behavioral phenomena during sleep: 13 in Group A (seven SW, six ST) with delta sleep-related episodes, eight in Group B with other parasomnias (six sleep bruxism and two SE), and six healthy controls. Classic sleep macrostructural parameters were no different in the parasomniacs and controls. Compared with the controls, our patients' sleep microstructure, scored by CAP analysis, showed increases in CAP rate (a measure of NREM instability with high level of arousal oscillation), in number of the CAP cycles, and in arousals with EEG synchronization, the increases being more significant in Group A than in Group B. An increase in sleep instability and in arousal oscillation seems to be a typical microstructural feature of delta sleep-related parasomnias and probably plays a role in triggering abnormal motor episodes during sleep in these patients.