OBJECTIVES: To quantify maternal perceptions regarding the quality of their child's diet, and to identify factors associated with misperceptions. STUDY DESIGN: A representative sample of 2287 children aged 2-5 years from a cross-sectional study (GENESIS study) was used. METHODS: Maternal perceptions of the quality of their child's diet, child's and mother's anthropometric characteristics, and other characteristics (i.e. socio-demographic and lifestyle) were recorded. The actual quality of each child's diet was estimated using the Healthy Eating Index (HEI) score. RESULTS: Based on the HEI score, 18.3% of participants had a 'poor' diet, 81.5% had a diet which 'needs improvement' and only 0.2% had a 'good' diet. Almost 83% of mothers overestimated the quality of their child's diet. The overestimation rate was 86% among mothers who declared that they choose their child's food based on what they consider to be healthy, and 72% among those who reported that other factors play the predominant role in food choices for their child (P<0.001). Moreover, total energy intake as well as the intake of fruits, grains, vegetables, meat and milk was significantly higher among children whose mothers overestimated the quality of their diet. CONCLUSION: The vast majority of mothers overestimate the quality of their child's diet. Given that maternal perceptions regarding the quality of their child's diet are likely to be one of the predominant factors determining the child's food intake, health professionals should make mothers aware of the existence of particular dietary recommendations that their children should meet in order to eat a healthy diet.