Behavioural sleep problems (childhood insomnias) can cause distress for both parents and children. This paper reports a model describing predictors of high sleep problem scores in a representative population-based random sample survey of non-Aboriginal singleton children born in 1995 and 1996 (1085 girls and 1129 boys) in Western Australia. Longitudinal repeated data were collected up to age 4 years by caregiver report. Children's sleep rhythmicity levels in their first year, as well as conflicted and lax parenting in their second year, predicted higher scores on the sleep problem scale from the Child Behaviour Checklist/2-3 in the children's third year. Higher scores on the sleep problem scale in the children's third year predicted higher scores on the aggressive behaviour subscale of the Child Behaviour Checklist/ 4-16. The results support a model in which sleep problems mediated the relationship between parental conflict and aggressive behaviour, even when controlling for maternal depression, which has been associated with children's aggressive behaviour.The most common sleep disorders among pre-school children are childhood insomnias or behavioural sleep problems, characterized by inability to settle to sleep, repeated waking with demands for parental attention, and waking early in the morning (Stores, 1996). Behavioural sleep problems can have a profound effect on children and their families. When Lam, Hiscock, and Wake (2003) compared children with and without current sleep problems they found that children with sleep problems had significantly higher mean scores on the *Correspondence to: