Lifetime prevalence, incidence, and risk factors for parasomnias were determined. Past experiences of non-REM, REM, and sleep-transition parasomnias were recorded. Diaries of night sleep duration, parasomnias, perception of aliens, levels of physical activity, headaches and intake of all substances, drugs, and tobacco were kept for 14 consecutive days. A total of 276 subjects were studied. Lifetime prevalences (95% CI) were 725 (668-776) for occurrence of any parasomnia, 43 (25-74) for sleepwalking, 112 (80-155) for sleep terror, 475 (416-533) for nightmares, 225 (179-277) for sleep paralysis, 43 (25-74) for sleep starts, 322 (270-380) for sleep talking, and 344 (291-402) for enuresis. Incidences (95% CI) were 210 (166-262) for occurrence of any parasomnia, 14 (6-37) for sleepwalking, 11 (4-31) for sleep terror, 170 (131-219) for confusional arousal, 18 (8-42) for nightmares, 14 (6-37) for sleep paralysis, 33 (17-61) for sleep starts, and 4 (1-20) for sleep enuresis. Multivariate analysis showed associations of increase occurrence of parasomnias and duration of sleep >7 h (p < 0.05) and intake of alcohol (p < 0.001), but heavy workload before sleep was associated with decreased occurrence of parasomnias (p < 0.01). Gender, smoking, caffeinated drinks, hypnotics, and headaches were not associated with parasomnias. Incidence of presence of aliens (95% CI) in the room was 25(0/infinity) (12-51). This study shows that more than 70% of the population have experienced parasomnias at any time in the past. Nightmares, enuresis, sleep paralysis and night terrors are the commonest parasomnias experienced in the past, while confusional arousal, sleep starts, and nightmares are the commonest parasomnias currently experienced. Incidence estimates show that all parasomnias persist into adulthood at reduced rates, but reduction of occurrence was greatest for enuresis. Long duration of night sleep and intake of alcohol predisposed subjects to higher occurrence of parasomnias.