OBJECTIVES: Our aim for this study was to determine the prevalence of dyssomnias and various parasomnias in early childhood and to describe their temporal evolution, gender differences, and correlates. METHODS: This research is part of a longitudinal study of child development. A randomized, 3-level, stratified survey design was used to study a representative sample of infants who were born in 1997-1998 in the province of Quebec (Canada). When the children were 2.5 years of age, 1997 families agreed to be interviewed. The presence of dyssomnias or parasomnias was obtained from a self-administered questionnaire that was completed by the mother at each round of measures. RESULTS: The percentage of children with frequent night wakings decreased steadily from 36.3% at age 2.5 to 13.2% at age 6. Similarly, the percentage of children who had difficulty falling asleep at night decreased significantly from 16.0% at ages 3.5 and 4 to 10% at age 5 and to 7.4% at age 6. The overall prevalence of each parasomnia for the period studied was as follows: somnambulism, 14.5%; sleep terrors, 39.8%; somniloquy, 84.4%; enuresis, 25.0%; bruxism, 45.6%; and rhythmic movements, 9.2%. Persistent somnambulism at age 6 was significantly correlated with sleep terrors and somniloquy. Persistent sleep terrors at age 6 were also correlated with somniloquy. Finally, persistent sleep terrors at age 6 were correlated with frequent night wakings. Separation anxiety was associated with persistent night wakings and with somnambulism, bruxism, sleep terrors, and somniloquy. CONCLUSIONS: There is a high prevalence of night wakings and sleep-onset difficulties in preschool children. Parasomnias are highly prevalent in early childhood and are associated with separation anxiety. However, they have little impact on sleep duration.