The 6-minute walk test (6MWT) is an established measure of exercise capacity in adults and children with chronic cardiac or respiratory disease. Despite its widespread use, there are no normal values for healthy children under 12 years of age. We aimed to provide normal values for children between 4 and 11 years. Healthy children were recruited prospectively from two UK primary schools and also children visiting Great Ormond Street Hospital. 328 children (54% male) aged 4 to 11 years were included in the study. Main outcome measures were the distance walked in 6 minutes, and oxygen saturation and heart rate during the 6 minutes and during a 3-minute recovery period. Mean oxygen saturation at baseline and during the 6MWT was 97-99%. Heart rate increased from 102+/-19 bpm at baseline to a maximum of 136+/-12 bpm. Overall, the mean distance walked in 6 minutes was 470+/-59 m. Distance walked correlated with age (r = 0.64, p<0.0001), weight (r = 0.51, p<0.0001) and height (r = 0.65, p<0.0001) with no significant difference between boys and girls. The distance walked increased significantly year on year from 4 to 7 years (4 years 383+/-41 m; 5 years 420+/-39 m, 6 years 463+/-40 m; 7 years 488+/-35 m; p<0.05 between each); further modest increases were observed beyond 7 years of age. Performing a 6MWT is feasible and practical in young children. This study provides data on normal children against which the performance of sick children and the response to therapeutic intervention can be judged.