OBJECTIVE: To examine the accuracy of maternal ability to classify their children's weight status correctly using a verbal and a visual classification instrument and to detect significant correlates of maternal misperceptions. DESIGN: Cross-sectional study. SETTING: Primary schools in four counties from north, west, central and south Greece. SUBJECTS: A representative sample of 1858 primary-school children aged 9-13 years was examined. Two different instruments to assess maternal perceptions of their children's weight status, i.e. a verbal and a visual one, were used. RESULTS: Verbal and visual maternal underestimation rates of children's weight status were 15·0 % and 41·3 %, respectively. The frequency of underestimation was much higher among overweight and obese children for both instruments. The highest underestimation rates of 87·9 % and 82·1 % in overweight and obese boys, respectively, were obtained with the visual instrument. Multiple logistic regression modelling revealed that the likelihood of both verbal and visual maternal underestimation of their children's weight status was significantly higher for overweight mothers and for those with a lower educational level. Furthermore, children's male gender and a nanny or someone other than the mother as the child's primary caregiver were found to increase the odds of visual and verbal maternal underestimation of children's weight status, respectively. CONCLUSIONS: The present study showed that the verbal instrument used to assess maternal perceptions of their children's weight status was more accurate compared with the visual one. However, both instruments showed that a considerable number of overweight and obese boys had their weight status underestimated by their mothers. Educating mothers to classify their children's weight status correctly might be a key factor for the implementation of successful childhood obesity prevention initiatives.