This study investigated the stability and change in teacher-reported problem behaviours across a four-year period. An epidemiological sample of 811 children aged 4-12 at the initial assessment was assessed twice with the Achenbach Teacher Report Form (TRF). We found medium stability in the level of TRF total problem scores. Highest stability was found for aggressive and other externalizing behaviours. Stability was higher for girls than for boys. Of the girls who could be regarded as disturbed at base line, 50% could still be so regarded four years later, whereas only 23% of the boys could be considered persistently disturbed across the study interval. Girls' scores on the Externalizing syndrome were especially stable.