A longitudinal study of the development of sleep patterns addressed the issue of continuity and change in night waking in the course of the first year. Mothers of 118 infants, who took part in a follow-up study of normal babies, completed a sleep questionnaire at 3, 6, 9 and 12 months. Regular night waking was a common characteristic throughout the first year (46% at 3 months, 39%, 58% and 55% respectively at 6, 9 and 12 months). The number of awakenings per night was a function of age. Following a decline in the number of interruptions from 3 to 6 months, an increase in night waking at age 9 months was recorded. Although the methodology does not lend itself to an objective validation of the changes in sleep-wake states, nor is it suitable for causal explanations, it is, nevertheless, important to note this profile. The increase in night waking towards the end of the first year coincides with significant socio-emotional advances which characterize this developmental stage.