Infants with slow weight gain cause concern in parents and professionals, but it is difficult to be certain whether such infants are genetically small or whether their energy intake is insufficient. The aim of the present study was to assess the impact of diet and feeding behaviours on slow weight gain early in infancy. The sample was 11 499 term infants from the Avon Longitudinal Study of Parents and Children (ALSPAC). A total of 507 cases of slow weight gain from birth to 8 weeks were identified and the remaining 10 992 infants were used as controls. It was found that infants who gained weight slowly between birth and 8 weeks were more likely to exhibit feeding problems such as weak sucking and slow feeding during this period. Feeding problems were substantially reduced during the recovery phase (8 weeks to 2 years) when these infants exhibited enhanced catch-up in weight. The proportion of mothers breast-feeding in the 4th week after birth was higher for slow weight gainers, but they were more likely to switch to formula at the start of recovery. During recovery, slow-weight gain infants had a slightly higher energy intake from formula and solids than controls. In conclusion, feeding problems seem to be the most important factors associated with the onset of early slow weight gain. Subsequently, a reduction of feeding problems and an increase in overall energy intake may contribute to their weight recovery. Health professionals should look for feeding problems in the first few weeks after birth and help mothers establish adequate feeding practices.