Background: The essential link between energy needs and energy intake is feeding behaviour, yet few studies have directly observed feeding behaviour in children who have failed to thrive. A cohort of 961 term infants was screened to identify children with first year weight gain below the 5th centile in order to examine their feeding behaviour and food intake. Methods: A nested case-control study was used with direct observation at 13-21 months over two lunchtime meals, one consisting of finger foods and the other of "spoon foods". Thirty children who failed to thrive and 57 controls were studied. The video-tapes were coded for feeding behaviour using a behavioural coding inventory which distinguishes between children feeding themselves and responding to being fed by their mother. The main outcome measures were counts of five feeding actions ("give, accept, feedself, refuse, reject") and measures of energy intake, the weight of food eaten and meal duration. Results: There were systematic differences in feeding behaviour between meal types, with mothers feeding their child more often at meals comprising spoon foods and children feeding themselves more often at meals comprising finger foods. By weight, more food was consumed at the spoon food meals, but energy intake was no higher, showing that the children compensated for the differing energy yields of the foods. Children who failed to thrive took in less energy than controls, and were less likely to sit in a highchair throughout the meal, but there were no clear differences in other aspects of feeding behaviour. Conclusions: Food type is an important variable when studying childhood feeding behaviour. Children who fail to thrive take in less energy than controls of the same age, despite there being no major differences in mealtime feeding behaviour.