A rating of parental concern was added to the Behaviour Checklist (BCL), which was then used as part of a Health Visitor administered routine developmental assessment of 1170, 3-year-old children. The overall prevalence of behaviour problems using a cut-off score of 10 was 10%, with 66% of parents having one or more concerns about their child. There were no sex differences. Parents of only children had more concerns on 6 of the 19 items even though their children behaved no differently from those with siblings. The usefulness of the BCL as a routine screening measure and the need to identify and address parental concerns at an early stage is discussed.