Weights were retrieved from child health records for an annual cohort of 3418 children, aged 18-30 months, to explore the relationship between deprivation and weight gain. Their level of deprivation was classified, using census data for their area of residence, as affluent (11%), intermediate (69%) or deprived (20%). Children from deprived areas were smaller at all ages with a widening gap: by one year of age, they were three times as likely as affluent children to be below the third centile for weight. The thrive index, a measure of the degree of centile shift, showed a slight gain over the first year in affluent and intermediate children, while in deprived children it decreased (p = 0.001). Deprived children were 2.2 times more likely than intermediate children to have failure to thrive, as manifest by subnormal thrive index values (p = 0.00008). Unexpectedly, children from affluent areas also showed slightly increased rates. We suggest that this may be explained by higher rates of breast feeding in affluent areas.