Objective: To investigate the relationships between weight reduction behaviour among non-overweight schoolchildren and dietary habits, perception of health, well-being and health complaints.Design: Analysis of the 2006 Health Behaviour in School-aged Children survey, a cross-sectional study involving schoolchildren aged 10-17 years.Setting: Schools in the Republic of Ireland.Results: The proportion of children (n 3599) engaged in weight reduction behaviour ('dieting' among non-overweight students) was 10.3%. Older children, females and those from higher social classes (SC) were more likely to report such behaviour. Non-overweight schoolchildren who reported weight reduction behaviour were less likely than those not engaged in such behaviour to frequently consume sweets, soft drinks, crisps and chips/fried potatoes (OR from 0.39 (95% CI 0.17, 0.89)) to 0.72 (95% CI 0.53, 0.99)); were more likely to consume diet soft drinks (OR 1.50 (95% CI 1.03, 2.18); and were more likely to miss breakfast during the week (OR 0.62 (95% CI 0.48, 0.80). The risk of subjective health complaints increased (OR from 1.47 (95% CI 1.13, 1.91) to 1.92 (95% CI 1.48, 2.49)); as did body dissatisfaction (OR 9.17 (95% CI 6.99, 12.02)), while perception of health and well-being decreased (OR 0.47 (95% CI 0.36, 0.61)) to 0.54 (95% CI 0.41, 0.70)). All analyses were controlled for age, gender and SC.Conclusions: Weight reduction behaviour among non-overweight schoolchildren is associated with considerable risk to physical health and emotional well-being. Since the risks associated with such behaviour varies by weight status, health professionals and researchers need to consider these issues in parallel.