Following a biopsychosocial model, the study investigated the role of child factors (gender, IQ), maternal factors (psychological distress, maternal education and vocabulary, maternal distress) and environmental factors (SES) in the relationship between language impairment and behaviour problems in preschool children. Participants were drawn from the Early Language in Victoria Study (ELVS) a prospective, longitudinal study examining the epidemiology and natural history of language impairment. The study reports on 1257 participants from the ELVS who completed questionnaires at 2 and 4 years and also completed face-to-face assessments at 4 years of age. Information was collected on child language, non-verbal cognition and social-emotional development; maternal vocabulary, maternal psychological distress and parent--child interaction; and SES. This study showed that language impairment is specifically associated with hyperactivity and peer problems but not anxiety and conduct problems at the preschool stage. Children with language impairment were at a higher risk for clinical levels of 'abnormal' behaviour which could lead to a psychiatric diagnosis than typically developing children. An examination of biopsychosocial variables associated with language and behaviour revealed that although language ability was a predictor of behaviour at both 2 years and 4 years of age, maternal distress was a stronger predictor of behaviour, with the association stronger for boys than for girls. Early intervention directed to children, especially boys, with language impairment deserves further attention, especially during the preschool period, in order to ameliorate the impact of language impairment on peer relationships and disruptive behaviour in later school years.