Infants’ sleep problems represent one of the most frequent complaints of parents consulting a pediatrician. In this large longitudinal study in Canada, sleep problems were tracked in children at 5, 17, and 29 months of age. As many as 24%, 7%, and 10% of children were sleeping fewer than 6 hours in a row at night at 5, 17, and 29 months of age, respectively. Putting the child to bed already asleep, feeding the child after a nocturnal wakening, bringing the child into the parents’ bed after a nocturnal wakening, cosleeping, and the infant’s temperament were all associated with not sleeping more than 6 consecutive hours at 17 and 29 months of age. Parent behaviors at bedtime and in response to a nocturnal wakening were highly associated with the child’s sleep habits.