BACKGROUND: Childhood obesity is a significant global health issue. National level data on long-term secular trends are relatively sparse. METHODS: Data were obtained from three large-scale surveys of school-aged children in Ireland involving measurements of height and weight in 1948, the 1970s and 2002. RESULTS: Significant increases in height and weight were observed in both boys and girls and in all age groups across the decades. The increases in weight were disproportionate to the trends in height. While boys aged 14 years were 23 cm taller 2002 than in 1948, their average weight was 61 kg, compared with 37 kg in 1948, an increase of 24 kg. A substantial proportion of the increase in weight is seen between the 1970s and 2002. CONCLUSIONS: The data provide stark and compelling evidence on the evolution of the obesity epidemic in Irish children in tandem with the increase in economic prosperity.