The aim of this prospective follow-up study was to assess the effects of pre- and perinatal factors on children's behaviour at the age of 3 years. Nulliparous women who attended a maternity health care clinic were invited to participate: 1443 women were included. Data were obtained from the mother, father, and clinic nurse. A Finnish translation of Achenbach's Child Behavior Checklist for Ages 2–3 was completed by 1086 families at the child's 3-year visit to the well-baby clinic. The results were analysed using Pearson's χ2, multivariate regression analysis, and coefficient of determination (100xr2). A good basic education (i.e. >9 years) of the mother and age over 25 years were associated with low syndrome-scale scores, indicating fewer behavioural problems. Poor health of the mother, a high number of pregnancy-related symptoms, and low Apgar scores for the newborn infant were associated with high syndrome-scale scores. In this population sample, the mother's health during pregnancy together with level of education, and marital status are more important in explaining the variation in a child's behaviour than biological risks during pregnancy.