A survey of senior infants in primary schools across Leitrim and part of Cavan has found a quarter are either overweight or obese.
Some 8 per cent of the children, aged five to seven, were actually obese.
The findings were presented at a conference hosted by the North-Western Health Board in Letterkenny yesterday, where the author of the study, Dr Christine McMaster, described them as worrying.
Her research was conducted among 361 children attending 44 primary schools in Leitrim and west Cavan in the 2001/2002 school year. Dr McMaster concluded there was "an urgent need to identify effective measures to prevent and treat childhood overweight and obesity".
She asked: "If this is the picture in a rural county, then what is the situation in more built up, heavier populated areas?"
She said the Leitrim findings were in line with preliminary results from other research projects carried out nationally.
Preliminary results from an all-Ireland study of 18,000 children aged four to 16 published last March indicated even higher rates of obesity in young children.
It found at least one in every three four-year-olds to be overweight.
The research, co-ordinated from University College Cork, found up to 35 per cent of four-year-old boys and 28 per cent of four-year-old girls were overweight. However, by age seven, slightly more girls than boys were found to be overweight. The figures indicated some 30 per cent of boys and 31 per cent of girls in this age group were overweight.
Dr McMaster warned that obesity results in ill health, both psychologically and physically. "And this is at enormous cost to individuals and society, not just in financial terms. Obese children tend to grow up to become obese adults and obese parents are more likely to have obese children," she said.