In this study, 65 obese children with a mean age of 12.1 years and mean relative weight (RW) of 156.1% had their lung function evaluated in comparison to predicted normal values. There were substantial changes in forced expiratory flow rates (FEF's) and maximum voluntary ventilation (MVV), with reductions to between 60% to 70% of predicted normal values. The more obese children (RVV greater than or equal to 150%) had significantly lower FEF's and MVV and a significantly greater proportion of the more obese children had FEF50 and MVV of less than 60% of predicted normal values. The results were suggestive of narrowing of small airways and increased respiratory inertance possibly due to excessive accumulation of fat in the chest wall and abdomen leading to respiratory limitation.