ABSTRACT As part of an ongoing longitudinal study of developmental delay (DD), 35 six‐year‐old children with delays of unknown aetiology were assessed with measures of cognitive, language and educational competence. Their parents provided detailed information about their self‐help and personal‐social competencies, behaviour problems and temperament. As a group, the DD children evidenced high rates of behaviour problems, but there was considerable within‐group variability in intensity and pattern of problems. Low relationships were found between the intensity of behaviour problems and children's chronological age (CA), IQ, language level and self‐help competencies. The child variable most strongly associated with behaviour problems was temperament, or behavioural style.